March 2014 - Vol:4 No:1 International S JOEURWNACL ofsewc-international.org/assets/sewcbook/mar-2014/pdf/1.pdf · Zahid Mohammad Mir, Mohammad Zahid Akhtar, Dar Dr. A.R 20 Reliable

�March 2014 | Journal of SEWC

Lessons to be Learned from Ancient Building Masters

Görün Arun, Prof. Dr.

Abstract

To achieve preservation in a building’s historical and cul-tural context, diagnostic studies for understanding the causes and mechanism of decay based on historical infor-mation, environmental monitoring, evaluation of the pres-ent level of safety and selection of appropriate preserva-tion methods and materials are indispensable scientific and technical basis for correct interventions.

This study is consisted of the construction methods and structural details design of master builders from various civilizations lived in Anatolia, the peninsula on far west of the Asia. Earthquake was always one of the most threat-ening actions to buildings in Anatolia. In order to make buildings safe, ancient building masters, using techniques developed by previous cultures, their own trial and error, and techniques transferred from one generation to anoth-er, sized the structural elements and designed their build-ings taking proper account of environmental actions. This paper is based on reviewing archaeological and history of architecture publications, discussions with archaeologists and experiences met during diagnosis phase of restora-tion works.

Introduction

The conservation and enhancement of the architectural heritage that represent the social, economic and environ-mental identity is a vital part of the future sustainability, and to the maintenance of social, economic and technical tra-ditions. Nevertheless due to aging, to the aggressive en-vironmental effects as earthquakes, soil settlements, etc., to increased loading as traffic vibrations, air pollution, etc. and to the fact that many old buildings and historic cen-ters were not maintained properly, a large part of this heri-tage suffers structural problems that menace the safety of buildings and people.

Vulnerability of ancient masonry structures to dynamic actions in seismic areas, are mostly due to the ageing, environmental factors and lack of knowledge in the inter-pretation of the building construction methods and details during intervention. The study of building construction method and structural details has a great importance in the mechanical and dynamic behavior of a building.

The decision making process of the preservation problem of these culturally valuable and potentially functional ar-chitectural structures should keep the structure’s original and authentic architectural message. It requires accurate evaluation procedures, efficient repair methods and ratio-nal design criteria. To achieve preservation in a building’s historical and cultural context, diagnostic studies for under-standing the causes and mechanism of decay based on historical information, environmental monitoring, evalua-tion of the present level of safety and selection of appropri-ate preservation methods and materials are indispensable scientific and technical basis for correct interventions.

The study of historical constructions oriented to their pres-ervation requires multidisciplinary teams of specialists formed in relation to the type and the scale of the problem (ICOMOS Charter 2003). And requires special technical and analysis tools adapted to the structure’s geometry, building materials and changes it had passed all through-out its lifetime (ICOMOS Charter 2003). Today, significant knowledge is available in modern testing and advanced analysis of heritage structures for the assessment of the failures. Constraints to be considered in the preservation of the architectural heritage are working together with a multidisciplinary team, the need of experienced profes-sionals who can collaborate with different disciplines and lack of knowledge in the interpretation of the building con-struction methods and structural details in the evaluation of structural problems for intervention decisions.

Historical documentations records should be investigated by experts and historians who are able to adequately in-terpret the ancient texts, in cooperation with the structural engineers, assisting the historian in the identification of structurally meaningful records. In investigating heritage buildings mostly constructed with the leading technol-ogy of its time and to understand their mechanical and dynamic behavior, it is important to take into account the engineering knowledge and practice of their construction time for proper interpretation of the causes of the failures and for decisions on proper intervention.

This paper points out the construction method and struc-tural details design of master builders from various civiliza-tions lived in Anatolia. Anatolia, the peninsula on far west

Journal of SEWC | March 2014�

of the Asia, was in the heart of cultural and trade routes of the Europe, Asia and Africa. This study is prepared through reviewing archaeological and history of architecture publi-cations, discussions with archaeologists and experiences met during diagnosis phase of restoration works.

Earthquake was always one of the most threatening ac-tions to buildings in Anatolia. Today, the seismic zone map of Turkey in 2007 Specification for Structures to be built in Disaster Areas, classifies the country into five seismic zones- in which Zone 1 is most severe. During the inves-tigation, it has been noticed that in seismic areas, the master builders introduced special techniques to make the structure withstand the lateral forces in substructure and superstructure. The ignorance of the accumulation of master builder’s knowledge and construction technique of their time may lead to incorrect intervention and long-term harmful effects on the structure. Besides, these techniques may give clues for the design of contemporary structures.

The main objective of this paper is to point out the impor-tance of acknowledging the design skills of master build-ers during diagnosis of the failures in historic buildings.

Building Masters

The ancient building master had to assume the roles of architect, structural engineer, mechanical engineer as well as the city planner and the contractor. The writings of the Roman architect Vitruvius and the studies on the previ-ous master builders as Ottoman Imperial architect Sinan, clearly demonstrate that “master builder” of the past was responsible for every aspect of creating a new building.

In order to make buildings safe, there exist several ancient construction code texts from Assyrians, Acadians and Hit-tites partly parallel to portions of the Hammurabi code, a well-preserved Babylonian law code, dating back to about 1772 BC. This Code of Hammurabi consists of 282 laws, with scaled punishments, adjusting “an eye for an eye, a tooth for a tooth” as graded depending on social sta-tus, of slave versus free man. In terms of Construction, it represents one of the oldest written standards. It is not a prescriptive code but some sort of a performance code, stating basically the punishment for failure in construction (Izquierdo - Encarnación, J. M., 2011). For example:

• If a builder build a house for a man and do not make its construction firm, and the house which he has built col-lapse and cause the death of the owner of the house, that builder shall be put to death.

• If it causes the death of a son of the owner of the house, they shall put to death a son of that builder.

• If it destroys property, he shall restore whatever it de-stroyed, and because he did not make the house which he built firm and it collapsed, he shall rebuild the house which collapsed at his own expense.

So, ancient building masters had to construct their build-ings firm to protect himself and his family members. How-

ever, the available technology and scientific knowledge were within the grasp of a single person. The tablets As-syrian building masters placed on important buildings, de-scribing each sequence of the construction (Sevin 1998), was one of the methods of transferring knowledge to the future generations.

These building masters, in creating buildings that still stand, used techniques developed by previous cultures, their own trial and error, and techniques transferred from one generation to another. Taking proper account of the environmental actions, were able to empirically size and design the structural elements.

Organization of Masonry Structural Elements

Masonry structuresare constructed of placing stone, brick (fired clay), adobe (sun-dried clay) or concrete blocks one over another or pouring moist earth adobe or concrete into a formwork in layers.If the structural elements are com-posed of placing the units one over another, these are laid dry, joined to each other with metal clamps or are laid in mortar. Resistance of a masonry building to exposed loads depends on the geometry of the structure, the strength and stiffness of the materials used, geometrical configu-ration of the units and the way the units are connected to each other. The masonry material’s high compressive strength and the friction resistance generated by the com-pressive action, helps masonry elements to withstand ten-sile stresses exerted by earthquake forces.

Connection of masonry units

As an Assyrian tablet mentions, masonry units have to move in order to dissipate energy(Sevin 1998). If the con-nection of the stone units is made with iron clamps, these clamps were laid in lead. Lead covered the iron, avoided corrosion of the iron and let the blocks move. If the stone and clay brick blocks are laid in mortar, using weak, rather than strong mortar let sliding along the bed joints dissi-pating energy so that the masonry unit will be safe. The mechanical property of the mortar changed according to the strength of the masonry unit. The ignorance of this knowledge and construction technique may lead to incor-rect interventions. NikaloasBalanos who led restorations of Parthenon from the late 1800s to the mid-1900s used iron clamps to hold the blocks of the columns together without coating them with lead. The damage caused by uncov-ered clamps has made it necessary to undertake several conservation interventions later. And recent earthquakes in Italy, Greece and Turkey showed that encaging masonry walls applying shotcrete damaged these walls severely.

Connecting walls with lacings

Thick masonry wall with two outer faces where the space in between is left empty or filled with rubble and mortar, the outer leaves are connected with suitable lacing at certain intervals to limit the support movements, to prevent wall bulging under gravity loads, to reduce the slenderness



ratio of the wall and to prevent crack initiation at another location. As lacing, timber or stone in brick walls, brick in stone walls was used. According to 1840 law in the form of building regulations, it was advised that the masonry build-ings will stand lateral forces better if they use metal ties. Afterwards, iron or copper ties were used as lacing.

Seismic Joints

In the building geometry, long projecting and different weighing components of a building has to be separated as expansion or seismic joints. Building masters also by not joining the masonry units to each other separated the building parts staying side by side. Such construction fea-tures may be incorrectly interpreted as damage. Different weighing parts of SüleymaniyeMosque in Istanbul and Da-vutpashaHammam in Skopje has two arches side by side belonging to different parts of the building (Fig. 3).

In many cases of archaeological excavations, it is seen that new structures have been built upon old foundations. Just as bricks and columns could be reused, so could foundation systems. In this case, the inner grillage founda-tion walls were not completely bounded to the perimeter wall foundation. When different components of a building were not of the same weight and would have settled dif-ferently, the intersecting lines of the foundations were not bounded.

Figure 1 Ties in the form of agrafe

These ties were joined to each other either with metal agrafe (Fig. 1), seen out of the wall or inserted in lead in a round clevis, not apparent from outside (Fig. 2). It is important to identify their place in order to assess the slenderness ratio of the wall. Slenderness ratio of a wall is very important in resisting earthquake forces.

Figure 2 Iron ties inserted in round clevis



Vaults and domes

Ancient building masters knew the geometry and behav-ior of the structural elements they constructed and pro-vided proper measures to exterminate the weaknesses. Some geometry of vaults as cylindrical and torus vaults and spherical domes inherently has tension at the skirts along one of their principal curves. To encounter the tensile stresses; building masters provided continuous boundar-ies as walls thickening or closely spaced arched columns or piers at the base. While thickening the area of tensile stresses, they used clay pipes in the area of compression to reduce the weight of the vault or dome. To construct a flat roof or a floor over these vaults or domes, they either emptied the space between the compression area of the vault/dome and the roof/floor surface or filled with ampho-ra not to give extra weight to the vault or dome surface (Fig.4). The steep vault with an elliptic parabolic surface which looks very similar to a pendantive dome and pa-raboloid dome has compression on both of its principal curves. In this case these surfaces didn’t necessitate any heavy portion. So, to make a flat roof, whole space be-tween the surface and the roof was filled with amphora or clay pipe.

Underground Water Drainage

Ancient building masters were aware that the water was the most serious non-seismic threat to masonry buildings in areas of both high and low seismicity. Depending on the porosity of foundation construction material and soil characteristics, it can damage the wall and soil by eroding away portions and by reducing the strength. To prevent weakening instability of the building through humidity re-sulted from underground water movement and to collect the surface water of rainfall; they designed an effective drainage system.

In archaeological excavations, it is seen that surface and subsurface drainage was given high priority during its de-sign and construction. The foundation rituals in Sumerian, Acadian (Lawson 2000) and Egyptian texts (Montet 1964) for temples, palaces, tombs, and forts actually consisted of marking the corners of the building with stakes and tying a cord to link them. In the morning, the priest represent-ing the Earth God loosed the cord so that it slipped down the stakes marking the limits of the building on the ground and started the first foundation trench of the building with a wooden hoe. Then the earth was cut through to the water table which represented the upper limit of the water god, Nun. Before starting the construction of the foundation, they constructed a well to unite the Water God to the Earth God. To reach the water table, sometimes they had to cut the rock layer. This construction system, constructing a well in the building, was practiced till late 19th century es-pecially in high seismic zones in Anatolia.

The major components of the drainage system to drain interior ground surfaces of a building included wells or cis-terns in the basement, galleries or channels that discharge

Figure 3 Double arches in Süleymaniye Mosque and DavutpashaHammam

Figure 4 Reducing the weight of the vault or dome

Kalenderhane (Striker et.al.1997)

Kizlar Mosque, Hasankeyf



the water out of the building, and gates for ventilation out of the building (Fig. 5). The size of the galleries or chan-nels connecting wells to each other or discharging water away from the building varies from 30-40cm to 1.0-2.5m depending on the size of the building. These are generally constructed of stones or bricks with mortar binding (Oust-erhoud 1999). These channels removed the moisture from surface and underground water, served to keep the struc-ture warm in the winter and cold in the summer. And dur-ing earthquake, they discharged the raising underground water avoiding soil liquefaction.

of the ambulatory, now filled with soil. YavuzSelim Mosque in Fatih district includes a large gallery heading toward a cistern that is blocked by the foundation of the mosque. There is also a cistern near the Fatih Mosque. In Ottoman settlements, the channels, penetrating the walls, generally continued to a nearby fountain tank.

Because this practice is completely forgotten demolished drainage system due to new constructions around the heritage structure is a frequently met phenomenon. Such blocking of the subsurface water control system causes water to rise to the building and soften the soil which leads to the building settlement. During diagnosis of the failures of the building, if this knowledge is ignored consolidation of the soil will not solve the problem.

During investigation in 1994, the piers of KüçükAyasofya Mosque- former Church of Sts. Sergios&Bacchos (527-536 AD) was in saturated form and the building had devel-oped many cracks due to the partial settlement. The envi-ronmental change as filling the sea in front of the mosque must have demolished the underground water discharging system. In restoration during 2004-2007, a well was found in the building and rectangular galleries were thought to be the places of rotten timber ties and filled with concrete. Now, piers started to get moisture again and have 70% moisture.

Foundation Organization

Foundations, as distributing the loads from superstructure to the earth below, have to resist compression, tension and shear stresses imposed by the soil pressure and earth-quake forces. The ancient building foundations of stone or brick masonry generally were deep to the hard soil. The foundations of the buildings usually didn’t pass the under-ground water level. The construction of foundation wall was either solid or three leaved wall, where the space between the two rows of stones is filled with the rubble and mortar or earth. Although the use of wood at the bases of founda-tion trenches was a standard practice, the use of wood ties in the cavity wall construction of the foundation has rarely been noted in the foundation systems. In the city walls of Istanbul, wooden grillage could be found in the walls.

The thick ancient building foundations were generally a vertical wall going deep to the hard soil. During the pro-cess of time as the wall thicknesses became thinner con-sequently the smaller sizes of foundation walls widening at the foot were practiced. If the wall was composed of closely spaced piers and there was not sufficient depth to step the foundations, sometimes inverted arches or vaults were made (Fig. 6). Soft soil was consolidated by timber piles. The foundation walls rested on timber mesh embed-ded in a khorasan mortar over these timber piles.

The foundation construction of the walls depends on the type of soil. The nature of the soil depends upon its grain structure and the geological way the soil was laid down. Acceleration, generated by ground displacements, is

Figure 4 Wells, gates, channels in the building

In settlements, the channels, penetrating the walls, gen-erally continued to the other building’s drainage system then was discharged to a channel along a main road or to a cistern or to a fountain tank. In most of the Byzantium buildings in and around Istanbul, the underground water was discharged to a cistern or the foundation of the build-ings included cistern. In Istanbul, in the area of Topkapı Palace, more than forty cisterns were found within the sub-structures of buildings (Eyice 1974). The twelfth-century the church of Pammakaristosincludes a large colonnaded and vaulted cistern that extends under the naos and parts


Journal of SEWC | March 201410

amplified or attenuated by the soil structure. To minimize amplification of acceleration input and prevent resonance, adequate construction would be stiff structure on soft soils, flexible structure on hard soils and rock. Generally, the old foundation systems that support the historical structures are different from the current practice in terms of mate-rials used and foundation organization. At high seismic zones, to provide the lateral stability of structures, building masters had introduced special techniques to change the natural frequency of soil.

If the rock bed or hard soil was deep, the foundation walls

rested on a pillow layer of sand, gravel or small stones as in Phaselis, Antalya (Fig. 7). If the hard soil was not so deep, the foundation walls rested on three layers of brick or stone blocks as in AlacaHöyük from Chalcolithic era (Nauman 1991), in Urartian buildings at east and Greek temples at the southwest of Turkey (Fig. 7). An Assyrian tablet writes that the soil was cut to the rock and the foundation was placed after filling the trench to 28 elbow height (Sevin, V. 1998). The foundations of masonry village houses at east Anatolia were constructed on a layer of ~40cm sand till 1960s. The thick layer of sand, gravel or stone pieces provided a change in the natural frequency of soil as well as adequate subsurface permeability to avoid a high water table condition (Arun 2009).

If the rock bed was close to the surface, a flexible base was provided by placing single or more layers of wooden grillage at the foundation base (Fig. 8). At the bottom of the foundation wall in Beycesultan, single layer of round wood grate projecting out 1.0-1.5m out from the foundation wall was laid side by side with small stones in between them (Nauman 1991). Foundation walls of a Byzantine chapel in Üsküdar, Süleymaniye Mosque from 16th C. (Aksoy 1982) and the inverted vault foundation of Edirnekapi Cistern from late 19th C. in Istanbul are constructed over 2 layers of wooden grillage laid perpendicular to each other. The foundation of Konjic Bridge, an Ottoman bridge in Bosnia & Herzegovina also contained two layers of wooden gril-lage laid in between two dolomite layers forming a platform for foundation footing (Sert 2007).

If the rock bed was on the surface, the rock was carved in the form of trough so that each stone of the foundation wall could be placed in the rock as if resting in a cradle (Nau-

Figure 6 Inverted vault foundation

Phaselis in Antalya

Urartian Castle in VanFigure 7 Pillow layer of gravel at Phaselis

Figure 8 Wooden grates of a Byzantine chapel and Konjic bridge


11March 2014 | Journal of SEWC

man 1991) (Fig. 9). In between the rock and the founda-tion stone; briar, pieces of coal or animal skin was placed (Pilinius 1601). Such rock foundations in the form of trough were often met in tells at southeast Turkey, in Boğazköy, a Hittite settlement at Middle Anatolia (Nauman 1991) and Temple of Diana at Ephesus (Ousterhoud 1999).

Another different foundation system practice was met at the 16th century octagonal tomb foundation of YavuzSe-lim Mosque complex. Around 4m distance away from the octagonal tomb, 6m high buried stone wall of 2m thick in the same octagonal form was found as if a retaining wall to absorb the first shock of earthquake forces (Fig. 10). Its effect on keeping the octagonal building from seismic forces has to be studied.

Conclusion

Ancient building masters, with accumulation of knowledge from previous cultures were able to size and design struc-tural system through;

• Connecting the masonry units properly so that they dis-perse energy

• Providing seismic joints by not connecting the different weighing components of a building

• Constructing vaults and domes taking into account of the stresses required by their geometry.

• Designing an effective underground drainage system• In EQ areas; changing the natural frequency of soil pro-

viding flexible base by placing a pillow layer of sand or gravel under the foundations, placing round wood layer at the foundation base; carving the rock in the form of a trough

Before making a decision on structural intervention it is in-dispensable to determine first the causes of damage and decay, and then to evaluate the safety level of the structure with experts of multi-disciplinary team (ICOMOS Charter 2003). In diagnosing the failures investigation of the histori-cal records is important. Historical documentations records should be investigated by experts and historians who are

able to adequately interpret the ancient texts, in coopera-tion with the structural engineers, assisting the historian in the identification of structurally meaningful records.

Ancient engineering systems are different than current practice ones. The knowledge of the old construction technique was lost during the last century. In investigating heritage buildings, it is important to take into account the engineering knowledge of their construction time. Ancient building masters had introduced special techniques to make the structure withstand the lateral forces and to con-trol the underground water movement. Ignorance of the master builder’s knowledge and construction technique may lead to incorrect intervention and long-term harmful effects on the structure.

Author Affiliation

Görün Arun, Prof. Dr.

Yildiz Technical University, Faculty of Architecture, Istanbul, Turkey

References

1. Aksoy, I.H. 1982. Foundation Systems Applied on Historic Structures in Istanbul Historical Peninsula, (in Turkish), ITU PhD Thesis

2. Arun, G. 2009. “Ancient Building Foundation Systems in Seismic Areas”, WiadomosciKonserwatorskie, Journal of the Association of Monument Conservators, nr 26/2009 pp: 278-288, ISSN 0860-2395

3. Eyice, S. 1973. “Byzantium Ruins in Degirmenaltı, Tuzla”, (in Turkish) SanatTarihiYıllığı 5

4. ICOMOS Charter 2003. Principles for the analysis, conserva-tion and structural restoration of architectural heritage, Rati-fied by the ICOMOS 14th General Assembly, in Vicoria Falls, Zimbabwe, October 2003

5. Izquierdo - Encarnación, J. M., 2011, “ Codes and Specifi-cations as Applied to Historic Preservation Projects”, WCCE-ECCE-TCCE Joint Conference 2, Seismic Protection of Cul-tural Heritage, Antalya, Turkey

6. Lawton, I. 2000. AncientMezopotamia, http://www.ianlawton.com/mes1.htm (28.03.2008)

7. Mamboury, E., Demangel, R. 1939. Le quartier des Manga-nes et la première région de Constantinople, Paris

8. Montet, P. 1964. “Le ritual de foundation des temples Egypti-ennes” Kemi 17 pp: 74-100

9. Ousterhoud, R. 1999. Master Builders of Byzantium, Princ-eton University Press, Princeton, New Jersey

10. PliniusSecundus, C. 1601. The Historie of the World. Book 37 translated by Philemon H.

11. Sert, H. 2007. “Konjic Bridge / Bosnia and Herzegovina”, Pro-ceedings of the Int. Symposium on Studies on Historical Heritage - SHH07,Antalya, Turkey

12. Sevin, V. 1998, Neo Assyrian Art- Architecture, (in Turkish) Publication of Atatürk Cultural Center

13. Striker, C., Kuban D., Berger, A. 1997.Kalenderhane in Istan-bul: The Buildings, Their History, Architecture and Decoration Final Reports on the Archaeological Exploration and Restora-tion at Kalenderhane Mosque, 1966-1978, Verlag Philip von ZabenGmbh, Mainz

(Nauman 1991)Figure 9 Foundation wall on rock

Figure 10 Retaining wall of the tomb at YavuzSelim Mosque



Durability of Self-Consolidating Concrete and Conventional Concrete Mixes Containing Different Types of Aggregates

Jamshid Esmaeili1, Jamil Kasaei2, Babak Atashfaraz3, Alireza Rostamimehr3

Abstract

Understanding durability as an essential part of the quality of infrastructures has become self-evident. Permeability is probably the most influential property related to the dura-bility of concrete infrastructures. In this paper, durability of self-consolidating concrete (SCC) and conventional con-crete (CC) mixes containing different types of aggregates is investigated. Different types of aggregates including natural river sand and gravel and also crushed rock and sand in dif-ferent ranges of water absorption and specific gravity were used in SCC and CC mixes that were prepared in water/powder and water/cement ratios of 0.42 and 0.47, respec-tively. The fresh properties of SCC were observed through slump flow time and diameter, V-funnel flow time and J-ring tests. Compressive strength, splitting tensile strength, and water permeability were measured in all SCC and CC speci-mens. It has been found that in a constant strength class, using aggregates with different properties has considerable effects on both workability and permeability of SCC and CC.

Introduction

Hardened cement paste and kind of aggregates are the most important parameters describing the initial structure of concrete {1}. Aggregates have a significant influence on rheological and mechanical properties and also on du-rability of concrete. Aggregate characteristics that are sig-nificant for making concrete include porosity; grading or size distribution, moisture absorption, shape and surface texture, crushing strength, elastic modulus, and the type of deleterious substances present {2}. Porous aggregates may increase the permeability of the concrete to ions and fluids, particularly if their pore system is interconnected. Ag-gregates with absorptions much higher than 2-3 per cent, should be treated as suspect and checked for their influ-ence on concrete performance. However, absorption limits are rarely specified in standards, although project-specific specifications may, if a suspect aggregate is likely to be used {3}. The choice of the appropriate type of aggregate for a given application is of primary importance as far as properties of concrete are concerned. Nowadays, many innovative and advanced concretes are used in different projects and concrete industry. Self-consolidating concrete (SCC) as an innovative concrete, has faced with great inter-est in concrete industry due to its unique properties. SCC

requires both high fluidity to flow under the effect of gravity alone and a good resistance to segregation {4}. It seems that the influence of aggregates type on properties of self-consolidating concrete should be significantly considered.

In this paper, durability of self-consolidating concrete (SCC) and conventional concrete (CC) is investigated regarding the types of aggregates. Different types of aggregates in-cluding natural river sand and gravel and also crushed rock and sand in different ranges of water absorption and spe-cific gravity were used in SCC and CC mixes that were pre-pared in water/powder and water/cement ratios of 0.42 and 0.47, respectively. Three types of aggregates with different properties were provided from different quarries to use in SCC and CC mixtures. The fresh properties of SCC were observed through slump flow time and diameter, V-funnel flow time and J-ring tests. Compressive strength, splitting tensile strength, and water permeability were measured in all SCC and CC specimens.

Experimental Details

Materials

Cement

The cement used in this study was type II Portland cement produced by Soufian Cement Company. This cement has the specific gravity of 3.15 and blain fineness of 2860 cm2/g. The chemical composition and physical properties of ce-ment are presented in Table 1.

Silica Fume

The silica fume used in this study containing 96% of sio2, was in conformity with ASTM C1240.

Aggregates

Different types of aggregates including natural river sand and gravel and also crushed rock and sand in different ranges of water absorption and specific gravity were used in self-consolidating concrete (SCC) and conventional con-crete (CC) mixes. Three types of aggregates with different properties were provided from different quarries to use in SCC and CC mixtures. Type-1 aggregates include gravel as coarse aggregate (CA) and natural river sand as fine aggre-gate (FA) that have higher quality (high specific gravity and lower water absorption). Type-2 aggregates include gravel


and crushed stone as coarse aggregate and crushed and river sand as fine aggregate that have lower quality (low specific gravity and high water absorption). Type-3 ag-gregates include crushed stone as coarse aggregate and crushed sand as fine aggregate that have lower quality (low specific gravity and high water absorption). The properties of different types of aggregates are presented in Table.2. The grading curves of different types of aggregates are il-lustrated in Fig.1.

Superplasticizer

The polycarboxylate-based superplasticizer (sp) admixture used in mixes with specific gravity of about 1.15 (g/cm3) and solid content of about 30- 40%.

self-consolidating concrete mix design was in conformity with ACI 237R07 {5}. Cement was replaced by Silica fume (5 percents) in all SCC mixes to provide required rheology and fresh properties. Different values of superplasticizer were used in SCC mixes to have the same target flow of fresh mixtures. To investigate the effect of aggregates type on concrete properties, the volume of aggregates was kept constant in both SCC and CC mixes. The cementitious ma-terials content (cement and silica fume) was kept constant in all concrete mixtures. The mixture proportions of all SCC and CC mixes containing different types of aggregates are presented in Table.3.

Mixture Prepration, Casting and Curing

Immediately after mixing of the concrete, the deformability and flowability of fresh SCC was evaluated using the follow-ing tests: slump-flow (mm), time required to reach 500 mm of slump-flow (s), time required to flow through the V-funnel (s) and passing ability through J-ring test. Workability of CC was determined using slump test (mm). The freshly pre-pared mixtures were used to produce 10*10*10 cm cubes for compressive strength test. The splitting tensile strength and water permeability of concrete were determined using 10*20 cm cylinders. After casting, all the specimens were kept in laboratory environment at 23± 2°C for the first 24h and then were stored in a water tank at temperature of 23± 1°C until the age of testing. The compressive strength was measured for 7, and 28 days. The average compressive strength of three cubes was considered for each age. The splitting tensile strength and water permeability were mea-sured at an age of 28 days. The average splitting strength and water permeability of three cylinders was considered at an age of 28 days.

Test Methods

The slump flow time and diameter, V-funnel flow time and J-ring tests were performed in conformity with EFNARC 2005 standards to determine the fresh properties of SCC mixes {6}. The water permeability test (water penetration depth) was determined according to DIN 1048, 2000 {7}. The compressive strength test was carried out in conformity with BS 1881: Part 116 at 7 and 28 days after casting {8}.

Cement type

l.o.I% SiO2% Al2O3% Fe2O3% CaO% MgO% SO3% K2O% Na2O%Blaine

(cm2/g)Compressive strength(kg/cm2)

3 7 28

Type II Portland cement

0.75 21.91 4.85 3.46 64.56 2.38 1.71 0.97 0.34 2860 179 274 370

Table1. Chemical composition and physical properties of cement

Type of Aggregates Surface texture of aggregates Specific gravity Water absorption (%) NMSa of CA(mm)

Fmb of FACA FA CA FA CA FA

Type-1 Gravel River sand 2.69 2.72 0.836 1.929 19 3.8

Type-250%Crushed stone

+50% Gravel50%Crushed sand +50% river sand

2.375 2.67 3.388 1.978 19 3.66

Type-3 Crushed stone Crushed sand 2.32 2.48 4.512 3.141 19 3.12a=Nominal maximum size, b=Fineness modulusTable2. Properties of different types of aggregates

Fig1. Grading curves of different types of aggregates: a) Type-1, b) Type-2, c) Type-3

(a)

(b)

(c)

Mixture Proportions

Different types of aggregates including natural river sand and gravel and also crushed rock and sand in different ranges of water absorption and specific gravity were used in SCC and CC mixes that were prepared in water/powder and water/cement ratios of 0.42 and 0.47, respectively. The

Durability of Self-Consolidating Concrete and Conventional Concrete Mixes containing Different Types of Aggregates


The splitting tensile strength test was performed at 28 days after casting according to ASTM C496/C496M {9}.

Results and Discussions

Fresh Properties

Flowability of fresh SCC is evaluated using slump-flow (mm), time required to reach 500 mm of slump-flow (s), time required to flow through the V-funnel (s) and passing ability through J-ring test. The workability of fresh conven-tional concrete mixes is determined using slump test. The results of fresh properties of both SCC and CC mixes are presented in Table.4. CC-3 and SCC-3 that are provided using crushed fine and coarse aggregates have the lower workability and flowability among CC and SCC mixes. As it can be observed, the superplasticizer dosage is increased as much more crushed aggregates are used in SCC mixes. However, despite the increase in superplasticizer content at SCC-3, its flowability is weaker than other SCC mixes. It seems that the angular shape and rough surface texture of crushed stone and sand decreases the workability of CC mixes and flowability of SCC mixes, considerably.

tional concrete. It is also observed clearly that the compres-sive strength of self-consolidating concrete mixes is higher than that of the corresponding conventional concrete mixes due to lower w/cm ratio and incorporation of silica fume in the mixtures.

Splitting Tensile Strength

The splitting tensile strength of conventional and self-con-solidating concrete mixes at the age of 28 days of water curing are illustrated in Fig.3. The strength values are the average of three test results. As it is seen in Fig 1, C-3 that is provided by lower quality aggregates has the lower splitting tensile strength in conventional concrete mixes. SCC-3 that is provided by lower quality aggregates has the lower split-ting tensile strength in self-consolidating concrete mixes.

Mix NoAggregates

TypeW/CM ratio

Cement(kg/m3)

Silica-fume(kg/m3)

Water(kg/m3)

Coarseaggregate (kg/m3)

Fineaggregate (kg/m3)

SP(kg/m3)

C-1C-2C-3

SCC-1SCC-2SCC-3

Type-1Type-2Type-3Type-1Type-2Type-3

0.470.470.470.420.420.42

436436436414414414

---

222222

205205205183183183

770684656770684656

939922870998981909

---

2.8343.6194.36

Table3. Mixture proportions of SCC and CC mixes containing different types of aggregates

Mix NoSlump(mm)

SlumpFlow (mm)

T500(Sec)

V-funnel(sec)

J-ring(mm)

SP(%)

CS-1CS-2CS-3

SCC-1SCC-2SCC-3

807040---

---

650620550

---

3.54.75.5

---

101322

---91020

---

0.650.83

1

Table4. Fresh properties of SCC and CC mixes

Compressive Strength

The compressive strength of conventional and self-consoli-dating concrete mixes at the age of 7 and 28 days of water curing are illustrated in Fig.2. The strength values are the average of three test results. As it is seen in Fig 1, C-3 that is provided by lower quality aggregates has the lower com-pressive strength in conventional concrete mixes. SCC-3 that is provided by lower quality aggregates has the lower compressive strength in self-consolidating concrete mixes. However, this reduction in strength values is not consider-able and the maximum decrease is about 18% and 12% at 28-days age for conventional and self-consolidating concrete, respectively. It can be seen that the compressive strength of self-consolidating concrete is less affected by aggregates quality in comparison with that of the conven-

Fig2. Compressive strength of CC and SCC mixes at 7 and 28 days age

However, this reduction in strength values is not consider-able and the maximum decrease is about 21% and 10% at 28-days age for conventional and self-consolidating con-crete, respectively. It can be seen that the tensile strength of self-consolidating concrete is less affected by aggregates quality in comparison with that of the conventional concrete. It is also observed clearly that the tensile strength of self-consolidating concrete mixes is higher than that of the cor-responding conventional concrete mixes due to lower w/cm ratio and incorporation of silica fume in the mixtures.

Permeability

Penetration of water and ions in concrete depends not only on concrete porosity but also on pore size, distribution, pore connectivity, and pore tortuosity {10}. Fig.4 presents the water permeability of conventional and self-consolidat-ing concrete mixes containing different types of aggregates. The water permeability test results are presented through both water penetration depth and water absorption of the specimens in 5 bar pressure. The results show that the self-consolidating concrete specimens have lower water


1�March 2014 | Journal of SEWC

permeability (lower water penetration depth and lower wa-ter absorption) in comparison with conventional concrete, regardless of the type of aggregates. This reduction in per-meability of SCC specimens is due to lower w/cm ratio and incorporation of silica-fume in mixtures.

As it is seen in Fig 1, C-3 that is provided by lower quality ag-gregates has the higher water permeability in conventional concrete mixes. SCC-3 that is provided by lower quality ag-gregates has the higher water permeability in self-consoli-dating concrete mixes. This increase in water permeability is very considerable and the maximum rise is about 122% and 44% at 28-days age for conventional and self-consolidating concrete, respectively. As it can be seen, the water perme-ability of self-consolidating concrete is less affected by ag-gregates quality in comparison with that of the conventional concrete. It can be due to better and improved pore struc-ture of the self-consolidating concrete that incorporates silica-fume in mixture and has lower w/cm ratio. However, incorporation of lower quality aggregates (with lower specif-ic gravity and higher water absorption) in both conventional concrete and self-consolidating concrete can lead to higher permeability and lower durability of concrete. Considering the strength properties of conventional and self-consolidat-ing concrete, it can be realized that the durability of both CC and SCC is much more affected by the aggregates quality in comparison with their strength properties.

Conclusions

Analyses of self-consolidating concrete and conventional concrete mixes containing different types of aggregates, al-lowed to conclude that:

• The angular shape and rough surface texture of crushed stone and sand decreases the workability of CC mixes and flowability of SCC mixes, considerably.

• Strength properties of SCC and CC mixes provided by lower quality aggregates (lower specific gravity and higher water absorption), are reduced. This reduction in strength properties is not considerable and is about 18% and 12% in compressive strength for CC and SCC and 21% and 10% in splitting tensile strength for CC and SCC, respectively.

• Strength properties of SCC are less affected by aggre-gates quality in comparison with that of the CC.

• Permeability of self-consolidating concrete specimens is lower than that of the corresponding conventional con-crete specimens due to lower w/cm ratio and incorpora-tion of silica fume in the mixtures.

• Water permeability of SCC and CC mixes provided by

lower quality aggregates (lower specific gravity and higher water absorption), is increased. This increase in water permeability is very considerable and is about 122% and 44% for CC and SCC, respectively.

• Water permeability of SCC is less affected by aggre-gates quality in comparison with that of the CC.

• Incorporation of lower quality aggregates (with lower specific gravity and higher water absorption) in both conventional concrete and self-consolidating concrete can lead to higher permeability and lower durability of concrete.

• Considering the strength properties of conventional and self-consolidating concrete, it can be concluded that the permeability and then durability of both CC and SCC is much more affected by the aggregates quality in com-parison with their strength properties.

Author Affiliation

Jamshid Esmaeili1, Jamil Kasaei2, Babak Atashfaraz3, Alireza Rostamimehr3

1Assistant Professor, Department of Civil Engineering, The University of Tabriz, Tabriz, I.R. Iran 2BSc, Concrete Technology Laboratory, Department of Civil Engineering, The University of Tabriz, Tabriz, I.R. Iran3BSc, Department of Civil Engineering, The University of Tabriz, Tabriz, I.R. Iran

References

1 J. Hoła, Arch. Civ. Eng. 38 (1992) 85–102.

2 Mehta, P.K. and Monteiro, P.J.M. (2006). Concrete Micro-structure, Properties, and Materials. McGraw-Hill Com-panies, Inc. New York.

3 M.G. Alexander and S. Mindess (2010). Aggregates in Concrete. Taylor & Francis, New York.

4 A PC. Cements of yesterday and today: concrete of to-morrow. Cem Concr Res2000;30(9):1349–59.

5 ACI Committee 237. Self-Consolidating Concrete. De-troit: American Concrete Institute; 2007.

6 EFNARC 2005, The European Guidelines for Self-Com-pacting Concrete: Specification, production and use, www.efnarc.org, 68 pp.

7 DIN 1048 (2000). Testing method for concrete – determi-nation of the depth of penetration of water under pressure.

8 BS 1881: Part 116: 1983. Method for determination of compressive strength of concrete cubes. British Stan-dards Institution, Her Majesty Stationery Office, Lon-don.

9 ASTM C496/C496M (2011). Standard test methods for splitting tensile strength of cylindrical concrete specimens.

10 EuroLightCon (1998). LWAC material properties state-of-the-art. In: Economic design and construction with light weight aggregate concrete. Brite-EuRam III, p. 47–8.

Fig3. Splitting tensile strength of CC and SCC mixes at 28 days age

Fig4. Water permeability of CC and SCC mixes at 28 days age



Retrofitting Safety Measures for Important Buildiings in Kashmir Valley

Zahid Mohammad Mir1, Mohammad Zahid Akhtar2, Dar Dr. A.R3

Abstract

The Kashmir valley falls in the active Himalayan belt and is one of the most earthquake prone regions of the world.In the past decade Kashmir valley has witnessed austere earthquakes with Magnitudes hitting up to (M 7.2) in 2005 which resulted in huge loss of life as well as enormous eco-nomic loss.The maximum fatalities were due to collapse of non-engineered constructions, amyriad of which happen to be masonry structures and thus aggrandized the prob-lem.Unfortunately, the seismic risk in developing countries like ours keeps on increasing because the basic princi-ples of earthquake resistant design and codal guidelines brought out by BIS are often not being followed in practice. The reasons are unawareness, apprehension of additional cost and intentional ignorance.New structures can easily be made earthquake resistant,however, the existing build-ing which need to be saved, calls for retrofitting.

The paper aims at in depth study of existing lifeline struc-tures (Health centers, schools etc.) in Kashmir valley and then applying scientific and technical know-how for struc-turalevaluation followed by adequate, easily implementable, economic retrofitting measures.The aim is also to make a user friendly retrofitting manual for common people, along with already completed Kashmir valley based lucid case studies so that it becomes easily adoptable by common man, thereby saving people from consultant charges, ex-plicating cost-comparison, and most importantly promot-ing engagement and awareness of earthquake safety and retrofitting. The paper contains detailed field work results and case study of major Health center and application of easy, simple retrofitting methods are proposed.

Introduction

Past earthquake statistics have shown us how extremely vulnerable the buildings are in the Kashmir valley. It also brought to light that when people build houses they do not seem to be aware of the threats posed by earthquakes. As it has observed in earthquake records, people are un-able to assess the root cause of earthquake destruction. The 2005 earthquake shook the confidence of Kashmiri`s in local building material and even in the techniques they

had been using to build houses for centuries. Immediate reaction has been a strong desire to abandon traditional architecture and building systems and adopt cement and steel bases construction in the local context.

Some structures were completely destroyed by the earth-quake. But many more were left standing, either dam-aged to varying degrees or with no damage at all. People in slightly damaged houses are likely to simply to patch up the damage and continue living in them. But those in moderately damaged houses often think that these are beyond repair and this want to demolish them and rebuild them.Kashmir has experienced earthquakes almost regu-larly during the course of its evolution and will continue to do so. Our traditional earthquake resistant architecture of Dhajji-Dewari and Taak is long gone and such have re-placed timber which was an essential building material with concrete.

Findings ofa leading scientist Roger Bilham of Colorado University issued a severe earthquake warning for Kashmir Valley. The scientist on the basis of GPS data compiled has conferred that a Magnitude 9 earthquake is eminent originating from the Zanskar Mountain Range. The scien-tist’s findings suggest massive loss of life given existing building codes. The reason he tends to suggest a loss of 3 lakh lives in the Valley is his belief on inadequate safety measures of existing infrastructure, codal provisions fol-lowed, disaster mitigation and disaster mitigation policies implemented.

In such a scenario it becomes very important for the people living in this part of the world to have their houses safe guarded against such ground shakings. It is surpris-ingly easy and cheap to produce realistic resistant to typi-cal seismic activity in building through proper Retrofitting schemes. As such this study envisages to address the se-rious and widespread problem of seismic vulnerability of buildings in the Valley with special attention to Hospitals, college and School buildings which has been assigned animportance factor 1.5 according to IS 1893.

For this purpose, Govt. Chest Diseases Hospital, Srinagar, has been selected as case study site.


In this study vulnerability assessment of the said structure has been carried out and appropriate economic retrofit-ting measures have been proposed. This paper presents a very placid and pragmatic coverage of the applicability of earthquake vulnerability assessment and retrofitting guide-lines as prescribed by BIS codes.

Vulnerability Assessment

Vulnerability assessment based on visual inspection was carried out for a myriad of important buildings in the Kash-mir valley by organizing regular field visits and taking re-cords at each site. Based on the data collected, buildings with considerably higher seismic vulnerability were short-listed and studied in detail.

The seismic vulnerability of a building depends upon the choice of building materials, the construction technology adopted, and the quality of the construction practice. In Kashmir, many types of construction practices are used with a variety of materials. These include local materials such as mud, straw, wood, stone, and bricks. Industrial materials such as concrete blocks, cement and steel are now also commonly used.

People in the Kashmir valley have an apprehension that including proper seismic concepts in the construction will increase the construction cost considerably. People are too bold not to even consult a proper civil engineer before construction, which ultimately results in vulnerable struc-tures posing a threat to life as well as to the property. The vulnerability of buildings in Kashmir can thus be very high, both with local and newly introduced materials. In the ab-sence of good construction practices and engineering in-puts even new buildings may be at risk. It is therefore very important to check the earthquake vulnerability of all exist-ing buildings of mixed traditional and modern construction in Kashmir; whether damaged or undamaged, since all of these are located in Seismic Zones IV or V.

This paper thus brings out easy to apply, economic retrofit-ting techniques for the use of a people of Kashmir. Practi-cal application of such retrofitting techniques have been explained and illustrated precisely in the two case studies that follow.

Case Study:Government Chest Diseases Hospital, Dal Gate, Srinagar

The Chest Hospital building Consists of various blocks like the Ward blocks, administrative blocks, Record section, Emergency ward, isolation ward etc. Some of the blocks are as old as 100 years and suffer serious visible damages and cracks, while some buildings like Administrative Block in comparatively young (around 20 years old) as shown in (Fig 1).

Prelimnary Evaluation

Preliminary evaluation was carried out and following data was obtained (table 1). The data was processed to assess

the vulnerability of the structure. The checklist and dam-age assessment is done according to handbook on seis-mic retrofit of buildings IITM.

Check List for Preliminary Evaluation of Masonry Buildings

{Ref. handbook for seismic retrofit of buildings IBC. IITM}

Building Name: Government Chest Diseases HospitalUse: HospitalAddress: Dal Gate, SrinagarNumber of Storey: 2 (for most of the blocks)Year Built:1990’sFoundation Type: Strip Footing Roof Type: Inclined SheetingFloor Type: Concrete FlooringStructural Components:- Beams, SlabsWall Type: RRSM Slab Thickness: -150 mm R/FThickness of Wall: 300 mmMortar Type: LimeVertical R/f bars: -Nil Seismic bands : - NilTable 1: Format of Preliminary Data Collection of Build-ings

Problem 1: Large Vertical Crack in Wall at Mid-Way (Grade 3 Crack)

Description and Cause of the Problem

Large vertical crack (G3 grade i.e. 5-10 mm wide) was seen in one of the buildings of the chest hospital. The crack was almost in the middle of the wall and was extending from roof to the plinth (Fig 2). A wall can be assumed to behave like a fixed beam as it is fixed at corners with other walls. As a result maximum sagging moment generally occurs at the mid-way of the walls. This can be a probable reason for the above type of the problem. The h/t and l/t ratios are as follows:

Fig 1: View of Govt. Chest Diseases Hospital, Srinagar



Remedial Retrofitting Measures

1. Make a ‘V’ notch along the crack; clean it with a wire brush.

2. Clean crack with water to remove the fine, loose par-ticles inside the crack.

3. Prepare masonry surface on both faces of the wall for fixing200 mm wide Ferro cement splices across the crack as shown in the diagram, by removing the plas-ter, raking the joints up to 12 mm depth, and cleaning it with water, extending on both sides of the crack to a minimum of 450 mm length.

4. Fill the crack with 1:3 cement mortar (non-shrink ce-ment: fine sand) with just enough water to permit push-ing in of mortar as far in as possible, from both faces of the wall.

5. Install the 150 mm wide 25x25 14 gauge galvanized welded wire mesh (WWM) (2.03 mm diameter) with 100 mm long wire nails inserted at spacing no greater than 300 mm in a staggered manner.

6. A gap of 10 mm must be maintained between the mesh and un-plastered wall.

7. Plaster over the mesh with two 12 mm coats of 1:3 ce-ment plasters.

8. Cure it with water for 15 days.

Problem 2:- G1 Grade Cracks at Many Places in the Building

a)Description And Cause

These G1 grade cracks (<1mm in width) in plaster are one-dimensional and are only measured in length (Fig 3). The reason might be when walls are held at corners by the adjacent walls and in the course of an earthquake when the shaking is perpendicular to a wall, its portion away from the corner will shake the most. Such shaking can result in

vertical cracks near the mid-length of the wall. The longer the wall the more it will shake, and the greater will be the chances of it cracking and suffering damage. Similarly, if a wall is extra high it will shake more. Such a wall will develop horizontal cracks when shaken.

a) Remedial Retrofitting Measures

Sealing of cracks using cement mortar should be carried out in the following steps.

1. Make a ‘V notch along the crack.2. Clean the crack with a wire brush.

Fig2: G3 Grade Crack in Wall

Thickness (t) Height (h) Length (l) h/t l/t

300 mm 3 m 8 m 10 26.67

(a)

(b)

(c)Fig. 3:Distresses: Fine cracks in various walls



3. Fill the gap with 1: 3 cement mortars. Finish the re-stored part to match the surrounding wall surface.

Problem 3: Possible Pounding Effects Between Two Parts Of The Building

struction of Govt. Chest Diseases Hospital. Although a lot of latest techniques are available today such as use of car-bon reinforced polymers (CRP), glass reinforced polymers (GRP), aramidic reinforced polymers (ARP), seismic wall-papers etcbut the cost of application of such techniques in a place like Kashmir valley is very high due to local con-straints such as, lack of skilled labour, materials and poor economic conditions. People already have a tight-fisted approach towards latest construction practice as a result people can barely resort to such retrofitting techniques. On the other hand, the proposed techniques use locally avail-able materials and do not need the involvement of highly specialized skilled labour. A normal Kashmiri mason is enough to do a commendable job using such techniques. Further this paper also aims to provide a practical vision to such cheap retrofitting techniques by discussing case study of the Hospital block.

It is hoped that the material presented in this paper will be useful in enhancing the understanding of masonry related earthquake engineering problems and use of seismic ret-rofitting.

Author Affiliation

Zahid Mohammad Mir1, Mohammad Zahid Akhtar2, Dar Dr. A.R3

1M.Sc Student, University of Stuttgart, Germany2B-Tech, NIT Srinagar3Head of Department, Civil Engineering Department, NIT Srinagar

References

1. A. Chakrabarti (2008), ‘Handbook on Seismic Retrofit of Buildings’, 12- 68.

2. Hamid A., Mahmoud A. and Abo El Maged S. (1994), ‘Strengthening and repair of unreinforced masonry structures: state-of-the-art’, 10th IB2MaC, Calgary, Canada, 485-497.

3. Hugo Bachmann (2003).‘Seismic conceptual design of buildings- Basic principles for engineers, architects, building owners, and authorities’, 7- 14.

4. Karantoni F. and Fardis M.(1992), ‘Effectiveness of seismic strengthening techniques for masonry Build-ings’, ASCE, 118(7), 1884-1902.

5. M. ElGawady (2004), ‘A Review of Conventional Seis-mic Retrofitting Techniques for URM’, 13th International Brick and Block Masonry Conference Amsterdam July 2004.

6. Matthys H. and Noland L., (1989), proceedings of an international seminar on ‘Evaluation, strengtheningand retrofitting masonry buildings’, TMS, Colorado, USA.

7. Rama Lakshmi (2011),‘Kashmir Underwater? A Colo-rado geologist thinks it is possible’,http://www.wash-ingtonpost.com.

Fig 4:Possibility of pounding between two adjacent buildings

Description and Cause

A new part of the building was constructed on offsets tak-en from the older part. Although separation joint was pro-vided between the two building parts but adequate space to avoid pounding was not provide (Fig 4). The roof level of the new part is at the mid was of the walls of the older part. In such a case, pounding between the two parts can result in severe damage.

Remedial Retrofitting Measures

The possible remedial measure in such a scenario is to remove a vertical layer of brick work in between the build-ing parts to account for possible pounding effects. How-ever, due precautions, such as, not more than exactly one brick layer should be removed in a manner that no dam-age should done to the walls,to preserve their structural integrity.

Problem 4:- Damage to Infill in Dhajji Walls

Description And Cause:

Infill in dhajji walls were seen to be damaged at many places in the buildings. The infill bricks were coming out at many places like the one shown in Fig 5.Damage to infill in Dhajji walls is accepted on account of possible energy dissipation in an event of an earthquake to conserve the integrity of wall as a whole.

Possible Remedial Measures

The damage infill should be replaced with fresh infill brick work.

Conclusion

This study is convergent on the common types of failures/cracks observed in the masonry and Dhajji-dewari con-



Reliable Design for CFRP-Strengthening of Reinforced Concrete Beams by Neural Networks Technique

Ibrahim M Metwally, PhD

Abstract

In the last years, a great number of experimental tests have been performed to determine the ultimate strength of rein-forced concrete (RC) beams retrofitted in flexure by means of extemally bonded carbon fiber-reinforced polymers (CFRP). Most of design proposals for flexural strengthen-ing are based on a regression analysis from experimen-tal data corresponding to specific configurations which makes very difficult to capture the real interrelation among the involved parameters. To avoid this, an intelligent pre-dicting system such as artificial neural network(ANN) has been developed to predict the flexural capacity of concrete beams reinforced with this method. An artificial neural net-work model was developed using past experimental data on flexural failure of RC beams strengthened by CFRP laminates. Fourteen input parameters cover the CFRP properties, beam geometrical properties and reinforce-ment properties; the corresponding output is the ultimate load capacity. The proposed ANN model considers the ef-fect of these parameters which are not generally account together in the current existing design codes with the pur-pose of reaching more reliable designs. This paper pres-ents a short review of the well-known American building code provisions (ACI 440.2R-08) for the flexural strength-ening of RC beams using FRP laminates. The accuracy of the code in predicting the flexural capacity of strengthened beams was also examined with comparable way by using same test data. The study shows that the ANN model give reasonable predictions of the ultimate flexural strength of the strengthened RC beams. Moreover, the study con-cludes that the ANN model predict the flexural strength of FRP-strengthened beams better than the design formulas provided by ACI 440.

Introduction

The use of fiber reinforced polymer (FRP) sheets as exter-nally bonded reinforcement is nowadays widely recognized as an efficient method for strengthening and upgrading re-inforced concrete RC members. In particular, the flexural strength of a reinforced concrete beam can be extensively increased by application of carbon, glass and ararnid FRP plates/sheets adhesively bonded to the tension face of the

beam[ l ]. In general, external reinforcement by FRP sheets is used for flexural strengthening, improving ductility, and shear strengthening. Over past few years, external strength-ening using FRP composites gained popularity over steel because of several reasons including material cost, light-weight feature, corrosion free and ease of application. At the same time, widespread experimental, numerical and analytical research has been carried out to understand and model the structural behavior of FRP strengthened re-inforced concrete beams. Particular awareness has been given to recognizing and understanding the failure modes that reinforced concrete beams retrofitted with FRP. There are three main categories of failure in concrete structures retrofitted with FRP that have been observed experimental-ly [2-4]. The first and second type consist of failure modes where the composite action between concrete and FRP is maintained. Typically, in the first failure mode, the steel rein-forcement yields, followed by rupture of CFRP as shown in Fig l(a). In the second type, there is failure in the concrete. This type occurs either due to crushing of concrete before or after yielding of tensile steel without any damage to the FRP laminate(Fig l(b)), or due to an inclined shear crack at the end of the plate(Fig 1(c)). In the third type, the failure modes involving loss of composite action are included. The most recognized failure modes within this group are de-bonding modes. In such a case, the external reinforce-ment plates no longer contribute to the beam strength, leading to a brittle failure if no stress redistribution from the laminate to the interior steel reinforcement occurs. Fig 1(d)-(g) show failure modes of the third type for RC beams ret-rofitted with FRP. In Fig 1(d), the failure starts at the end of the plate due to the stress concentration and ends up with de-bonding propagation inwards. Stresses at this location are essentially shear stress but due to smal1 but non-zero bending stiffness of the laminate, normal stress can arise. In Fig. 1(e), the entire concrete cover is separated. This failure mode usually results from the formation of a crack at or near the end of the plate, due to the interfacial shear and normal stress concentrations. Once a crack occurs in the concrete near the plate end, the crack will propagate to the level of tensile reinforcement and extend horizon-tally along the bottom of the tension steel reinforcement. With increasing external load, the horizontal crack may


propagate to cause the concrete cover to separate with the FRP plate. In Fig. 1(f) and (g), the failure is caused by crack propagation in the concrete parallel to the bonded plate and adjacent to the adhesive to concrete interface, starting from the critically stressed portions towards one of the ends of the plate. It is believed to be the result of high interfacial shear and normal stresses concentrated at a crack along the beam. Also mid span de-bonding may take concrete cover with it.

culated and the obtained flexural capacity. For example, some design guidelines and codes ignore the influence of the length of FRP sheet, concrete compressive strength, and concrete cover in tension zone on prediction of ulti-mate flexural capacity. These are the major assumptions that cause divergence towards the experimental results, Since the ultimate flexural behavior of strengthened RC beam is affected by many factors and parameters, artificial neural network (ANN) method can be used as an effective tool to predict the ultimate flexural behavior of strength-ened RC beams[ 10- 14]. The proposed ANN model con-siders the effect of various parameters (Table 1) which is not generally account together in existing design codes. ANN model contains data for both application schemes. Eighty three(83) experimental data of CFRP-strengthened RC beams were collected from literature. As it is aimed to suggest a practical ANN model, the mechanical proper-ties of strengthening material and mechanical and dimen-sional properties of beams are selected as inputs( Table 1 ). The predicted ANN results are primarily compared with experimental CFRP contributions of strengthened beams and then with the predicted results of theoretical guideline equation by American guidelines ACI 440 [5]. It was cho-sen among all current design codes, because it attained the best prediction of flexural capacity of FRP-strengthened RC beams as reported by Al-Zaid et al.[ 15]. Performed analysis showed that the neural network model is more ac-curate than the ACI 440 guideline equation with respect to the experimental results and it can be applied satisfactorily within the range of parameters covered in this study.

Experimental Technique and Data

An extensive literature review has been carried out and eighty three(83)RC beams strengthened in flexure with CFRP laminates were collected from the published lit-erature. These test results are used to provide the ex-perimental data for ANN. The all tested beams are sim-ply supported and subjected to two point loads acting symmetrically with respect to the centerline of the span as shown in Fig. 2. This case provides a larger amount of data, which is essential for better training of a network. During the collection of the data, specimens that do not have flexural failures have been excluded from the training set. The selected specimens covered all modes of failure of flexurally -strengthened RC beams with CFRP laminates as mentioned above. The basic parameters that control the ultimate load of beams, based on previous research works are listed in Table 1. The experimental data include 83 beam results, which are taken from the tests carried out by references [16-36] as shown in Appendix A. The data

Fig. 1- Failure modes in beam retrofitted with FRP sheets in flexure[2-4]

This paper proposes the new approach to the problem, using an empirical model developed from observations of the actual performance of laboratory beams. Specifically, a neural network approach is proposed due to its proven abi1ity to solve problems of this type. That is, problems requiring the rapid generation of solutions, the accurate modeling of functions that are non-linear, and comprise many poorly defined independent variables. The objec-tive was to determine the viability of using this approach to obtain accurate predictions of the maximum strength of externally CFRP-strengthened RC beams. As an added advantage, the neural network approach was expected to make predictions of beam performance within a fraction of a second. This, in turn, would make it possible to evaluate a very large number of alternative external reinforcement configurations, and thus determine a more optimal design solution. The success of experimental studies produced growing demand for analytical investigations since predict-ing the ultimate flexural strength of the strengthened RC structures is crucial. Therefore, several proposed analyti-cal formulations have been developed to guide the design, detailing and installation of FRP based systems [5-9]. The developed analytical equations estimated the contribution of FRP reinforcements within certain limits but not accu-rately in some cases. The assumptions that were made while designating the behavior of the strengthened speci-men did not resemble to actual behavior due to some spe-cial situations and that cause the calculated results to be different from the obtained flexural capacity. There are sev-eral parameters that cause differences between the cal- Fig. 2- Typical FRP-strengthened RC beam



are rearranged in such a way that 14 basic parameters are listed as input values, and the ultimate load is included as the corresponding output targets (Table 1). There is no single design code that considers all these parameters.

Analytical Study

Neural Network Model of CFRP- Strengthened Beams

An artificial neural network (ANN) is a simplified math-ematical model or computational model that tries to simu-late the structure and/or functional aspects of biological neural networks for engineering problems. It contains an interconnected group of artificial neurons and processes information using a connectionist approach to computa-tion. In most cases, the ANN is an adaptive system that changes its structure based on external or internal infor-mation that flows through the network during the learn-ing phase and can be used as a prediction tool for cases where the output solution is not available. Modem neural networks are non-linear statistical data modeling tools. ANN contains three main sections which are classified as, input layer, hidden (inner) layer, and the output layer. Input parameters are presented in the input layer and the solu-tion of the problem are evaluated with the output layer. In between these layers, hidden layer is placed and provides help to the network in the learning process. The number of neurons of the input and output layers are determined in order to represent the characteristic of the existing prob-lem accurately. Hidden layers can be formed with one or more layers and the number of neurons in the hidden layer is determined by the users. The number of the neurons in the input layer is equal to the number of the independent variables in the experiment as shown in Table l . The num-ber of the hidden layers and the number of the neurons in each layer is chosen to provide a minimum value for the error between the measured output and the network’s output while maintaining the ability of the network to gener-alize. In the current research, Feed-forward back-propaga-tion neural networks (FBNNs) were applied for prediction the capacity of strengthened beams with one input layer (it contains 14 independent variables (Table l )that may affect the flexural capacity), one hidden layer have 20 neurons, and one output layer was designed to predict the flexural load capacity. The TRAINLM training function available in MATLAB Neural Toolbox [38] was used to train the network using the LERNGDM adaption learning function. The input data was divided into three sets. The first set consists of 70% of the data is used to train the network. The second and third sets, each consists of 15% of the data are used to validate and test the generalization ability of the net-work, respectively. Several architectures were tried and the one that gave the least error was chosen(Fig. 3). The se-lection of optimal configuration of ANN is the key point to achieve successful results from the suggested ANN mod-el. Therefore, the mechanical properties of strengthening material and mechanical and dimensional properties of ex-perimental beams are selected as inputs. In the literature, the strengthened specimens have concrete strength is

generally above 20 MPa. In addition, some guidelines [30] do not propose to use FRP strengthening technique (due to the bond problems) to the structures with compressive strength below 17 MPa. However, the concrete strength of buildings that require retrofitting is generally lower than the pre mentioned value. In this study, the structures that have low concrete compressive strength are also accounted in the proposed ANN model in order to achieve the aspects of strengthening philosophy. Therefore, experimental data that will direct ANN model to evaluate such structures was especially collected from literature. The neural network model is built by considering these approaches and it contains fourteen input nodes (Table 1). The optimum net-work is selected based on minimum error and maximum correlation coefficient between data. The properties of the selected network are shown in Table 2.

In this section, an experimental database(consists of 83 RC beams strengthened with CFRP sheets in flexure) is used to investigate the accuracy of ACI 440, and train and test the ANN model in the prediction of the flexural load of RC beams. The results of the ANN model are com-pared with ACI 440 empirical code, based on calculat-ing the mean(M), standard deviation(STD), coefficient of variation(COV), and variation(VAR). Also, the R2 of the lin-ear regression line for the predicted values by both ANN model and ACI 440 code are determined.

Fig. 4 shows the relationship between the experimental data and the training, validation and testing sets. It can be shown that the relationship between the complete set of the experimental data and the data predicted by the neural network is excellent.

To show the efficiency of the proposed ANN model, the experimental database are used and the flexural load of CFRP-strengthened RC beams is calculated using ACI 440 formula and ANN model. Also, to evaluate the perfor-mance and accuracy of the ACI 440 and ANN, values of the flexural capacity from ACI 440 design code and ANN are compared with measured experimental data. Com-parisons between observed (experimental) and predicted flexural load are shown in Fig. 5. It can be seen that the predicted loads by ACI 440 are more scattered from the experimental ones compared to ANN predictions.

To show the superiority of proposed ANN model, the mean(M), standard deviation(STD), coefficient of variation(COV), variation(VAR), and R2 values for ANN model and ACI 440 code are presented in Appendix A and Fig. 5 . Comparison of the results indicates that the ANN model has satisfactory values of R-square and M( close to one) and a lower value of STD, COV and VAR, so that its performance is more accurate. Also, the ANN model performs a much better prediction, compared with ACI 440 empirical code.

Fig. 5 shows a linear regression between the experimental and the neural loads. The agreement is excellent as at-tested to by the R2-value (0.98) of the regression analy-sis and descriptive statistics (Mean=1.01, STD=0.15,



COV=15.12, VAR = 0.02) it means that the prediction by neural networks have a smallest coefficient of variation, smallest scatter and better confidence intervals compared with ACI 440 (Mean=1.09, STD=0.25, COV=22.68, VAR = 0.06) as reported in Appendix A. ACI 440 produced nearly close predictions to the experimental results. However, at almost every step they underestimated the experimental results and this shows that their predictions are always on the safe side because of the safety factors that were used while calculation.

dividing the weights by the sum for all the input param-eters, which gives the relative importance for each input parameter to output parameter. The relative importance for various input parameters are shown in Fig. 6. As the figure indicates, the major important and influencing pa-rameters are the beam depth (18.8%) and length of CFRP sheet (16.1) while the most of other input parameters has insignificant importance on the predicting of ultimate load (10.6%-0.7 %). Beside the beam depth and length of CFRP sheet , six parameters were select from the residual twelve parameters,( which have importance more than 5% which is considered as the min limit as reported by Yousif and Al-Jurmaa(39)) , these are (As, cov , fc , b , fy , and Es).

Input no. Parameter Symbol Minimum Maximum

Inputs

1 Concrete cylinder comp. strength, MPa f’c 18 55.2

2 Width of beam, mm b 100 500

3 Effective depth, mm d 50.8 419

4 Effective span, mm l 1400 5000

5 Area of tension reinforcement, mm2 As 71 2413

6 Area of comp. reinforcement, mm2 A’s 28 1609

7 Yield strength of steel rfts, MPa fy 335 590

8 Modulus of elasticity of of steel rfts, GPa Es 165 201

9 Concrete cover in tension side, mm cov 15 55

10 No. of CFRP layers nf 1 4

11 Modulus of elasticity of CFRP sheet, GPa Ef 11 240

12 Width of CFRP sheet, mm bf 25 480

13 Thickness of CFRP sheets, mm tf 0.11 6

14 Length of CFRP sheet, mm lf 1200 4800

Output no. Output

1 Ultimate flexural load, kN Pu 16.1 669.3

Table 1- Range of input parameters and output variables

No. Parameter Property

1 Network functionFeed-forward back-propa-

gationR

2 Network architecture 14-20-1

3 The number of training data 59 0.99

4 The number of verifying data 12 0.99

5 The number of testing data 12 096

6 No. of all data 83 0.99

Table 2- The Network Properties

Influencing of Input Parameters

Because the weight of the network cannot be easily under-stood in the form of a numeric matrix, they may be trans-formed into coding values in the form of a percentage by

Fig. 3- Artificial Neural Network Structure

Fig. 4 - Regression analysis for training, validation, testing, and whole data



Fig. 7 also present the experimental-to-calculated flexural load versus d, lf, As, cov, fc, b, fy, and Es, from this figure, it is evident that the level of accuracy of the ultimate flexural load predicted by the ANN model seems to be consistent with the varying the various parameters. The proposed model has been compared to the current design guide-lines provided by ACI 440. More accurate and consistent

predictions have been obtained using the model produced by ANN.

Conclusions

The following conclusions can be drawn based on the per-formed analyses and comparisons reported in this paper:

1. In this study, a Feed-forward back-propagation neural network with fourteen input neuron, twenty hidden neu-rons and one output neuron was developed to intro-duce a reliable flexural design of CFRP-strengthened RC beams with high accuracy. Results show that the ANN model provided a better prediction of flexural load than the ACI 440 model and is more accurate. In ad-dition, the predictions of ANN model were distributed around experimental results, while ACI 440 was more scattered from experimental results, indicating that they predominately under-estimate the flexural capacities.

2. The proposed ANN model provides the most accurate results in calculating the ultimate flexural load. It con-siders the effect of various 14 parameters which is not generally account together in the current existing de-sign codes.

a) ACI 440 Formula

b) ANN ModelFig. 5 - Comparison Between Experimental and Predicted Flexural Capacities

Fig. 6- Relative Importance of Input Parameter for ANN Model

Fig. 7 - Experimental to predicted ultimate flexural loads of CFRP-strengthened beams versus d, lf, As, cov, fc, b, fy, and Es respectively



3. The effective beam depth and length of CFRP sheet are the major important and influencing parameters that affecting the prediction of the ultimate load capac-ity of RC beams strengthened with CFRP sheet.

4. Some guidelines do not propose to use FRP strength-ening technique (due to the bond problems) to the structures with compressive strength below 17 MPa. However, the concrete strength of buildings that re-quire retrofitting is generally lower than the pre men-tioned value. Therefore, an ANN model is developed by considering the need of retrofitting structures with low concrete compressive strength in this study. Accord-ingly, obtained results showed that ANN model can successfully predict the FRP contribution for structures with low concrete compressive strength within accept-able limits.

Author Affiliation

Ibrahim M Metwalls, PhD

Assoc. Prof., Concrete Structures Research Institute, Housing & Building Research Centre, Egypt

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A Taguchi Approach for Investigation of Mechanical Properties of Recycled Aggregate Concrete Containing Nano-Silica

Prusty R1, Mukharjee B.B2, Barai S.V3

Abstract

The objective of the study is to analyze the mix proportion parameters of concrete containing recycled aggregates and Nano-Silica using Taguchi’s experimental design methodology for optimal design. For that purpose, con-crete mixtures according to the L9 (34) orthogonal array are designed with four factors with each one having three different levels. The chosen factors are Water cement ratio, Replacement of Natural Coarse Aggregates with Recycled Coarse Aggregates (%) or Recycled Coarse Aggregate (%), Maximum cement content (kg/m3) and Replacement of Cement with Nano-Silica (%) or Nano-Silica (%). Com-pressive Strength, Split Tensile Strength, Flexural Strength and Modulus of Elasticity test are performed and results are analyzed as per Taguchi’s experimental design meth-odology. The analysis depicts that all selected factors are significantly affecting the test results; however, Water ce-ment ratio and Nano-Silica (%) are more dominant than others factors. Moreover, the results of verification experi-ments depict that difference between the predicted values and experimental results are not significant.

Introduction

Construction is not known to be an environmentally friendly activity since it causes several problems such as depletion of natural resources, environmental pollution and shortage of landfills for waste disposal. Therefore, recycled aggre-gates produced by crushing waste concrete generated from the concrete demolition of aged concrete structures have currently received growing attention, due to its prob-able utilization in construction of environmentally friendly concrete structures. Moreover, the lack of natural aggre-gates for production of concrete leads to generate recycled aggregates as alternative fillers in several countries (Oiko-nomou, 2005). Recycled aggregates are manufactured by undergoing a series of operations like crushing, grinding and screening of waste demolished concrete. Recycled aggregates may be Recycled Coarse Aggregates (RCA) or Recycled Fine Aggregates (RFA) based upon their gra-dation. The concrete produced utilizing these recycled ag-gregates in place of natural aggregates are called Recy-cled Aggregate Concrete (RAC). However, the use of RFA

as replacement of natural sand for production of concrete is not productive as their uses weaken the performance of concrete (Buyle-Bodin and Hadjieva-Zaharieva, 2002). The RCA particle is always considered as a small piece of concrete since it composed of original coarse aggregate (OCA) and attached mortar (AM). The above-mentioned old attached mortar was porous in nature and primarily responsible for inferior properties of RCA such as higher water absorption and lower density as compared to that of NCA (Juan and Gutiérrez, 2009). Therefore, the concrete produced using these RCA are having inferior properties compared to NAC. Several investigations are conducted to determine the behavior of RAC and some are discussed below.

Nixon (1978) reviewed the research papers available in the area of use of recycled concrete aggregates for the production of new concrete and stated that compressive strength of concrete produced with recycled aggregates had lower than that of the source of the concrete from which aggregates were produced. Moreover, the general relation could not be drawn between the compressive strength of recycled aggregate concrete and that of parent concrete. Hansen (1986) stated that the Compressive Strength (CS) of RAC was found to be 5-10% lower than that of analo-gous concrete produced with natural coarse aggregates (NCA). However, CS of NAC and corresponding RAC pro-duced with the similar water-cement ratio might vary to the extent of 50% or more based upon the quality of the waste concrete from which the aggregates were retrieved. Other researchers reported that that compressive strength of concrete containing 30 % RCA remained unchanged but subsequently CS started reducing with increasing percent-ages RCA (Limbachiya et al., 2000). The investigation on the behavior of the concrete produced with recycled aggre-gates retrieved from laboratory specimens was conducted and it was reported that the properties of parent source of concrete had significantly affecting the CS of recycled aggregate concrete (Ajdukiewicz and Kliszczewicz 2002). Furthermore, it was possible to produce RAC with higher compressive strength than the source concrete from which aggregates were derived for instance RAC having 28 days CS 80 MPa could be generated using aggregates manu-factured from parent concrete having 28 days CS 60 MPa.


The source from which these RCA were retrieved had an important role in determining the properties of RAC. Poon et al.

(2004) carried out investigation on concrete made of two different types of RCA: one derived from a normal con-crete and other from a high strength concrete. The out-come of the study revealed that the concrete produced with the recycled coarse aggregates retrieved from a source of high-performance concrete developed higher compressive strength at all tested ages than the con-crete prepared with aggregates manufactured from the recycled normal-strength concrete. This difference in CS of both types of concrete was attributed to the presence of a denser relatively dense interfacial zone in the high-performance recycled aggregate concrete compared to a loose and porous product layer filled the normal-strength concrete interfacial transition zone. However, the 90 days CS of RAC consisting of aggregates retrieved from a source of high-performance concrete reached the level of that of NAC produced with crushed granites. Padmini et al. (2009) investigated the effect of mechanical properties of parent concrete on the characteristics of the recycled aggregate concrete. It was concluded that compressive strength of RAC produced from the aggregates retrieved similar strength increases with maximum size of aggregate because the amount of old attached mortar present in re-cycled aggregate increased with the decrease in the maxi-mum size of aggregate, which resulted in higher reduction in strength of RAC. Moreover, the CS of RAC improved with increase in CS of parent concrete for a particular size of aggregate however, for a specified strength of RAC, the achieved compressive strength reduced with an increase in the strength of parent concrete from which the recycled aggregates were retrieved. This variation of compressive strength of RAC was because of the increase in amount of adhered mortar in recycled aggregates with increase in the compressive strength of parent concrete irrespective of the size of aggregate, which had an influence in determining the strength of RAC. Poon et al. (2004) investigated the in-fluence of moistures states of aggregates on the compres-sive strength of RAC and it was recommended that the not to use the recycled aggregate in the Surface saturated sur-face-dried (SSD) state for production of concrete. More-over, the compressive strength of RAC made of oven dried (OD) recycled aggregates were more than that of concrete made with saturated surface-dried aggregates. Based on the results of this investigation, it was concluded that the concrete prepared with the recycled coarse aggregates of the state of Air Dried (as received) and its quantity not more than 50% produced optimum result. Tam and Tam (2008) demonstrated that ITZ between cement mortar and recycled coarse aggregate plays a vital role in determin-ing tensile behavior of concrete. Moreover, the ITZ of RAC could be divided into parts, one between RCA and new paste (new ITZ), and the other between the original coarse aggregate and old attached mortar (old ITZ). The presence of many minute pores and cracks in attached old cement

mortar absorbs some part of mixing water, thereby, reduc-ing the amount of water available for hydration at ITZ for RAC. Therefore, RAC exhibited higher porosity, less den-sity and higher absorption rate leading to poorer in tensile strength, as RAC could not able to achieve the designed requirements as that of normal concrete. Tabsh and Ab-delfatah (2009) reported that about 25-30% reduction in tensile strength in comparison to NAC was observed in case RAC made with aggregates retrieved from a concrete of 30 MPa or RCA obtained by crushing concrete from un-known source. However, this margin is reduced to a range of 10-15% for the concrete made with RCA produced by crushing 50 MPa concrete.

From aforementioned studies, it could be concluded that mechanical properties of RAC were inferior to NAC. Therefore, several techniques were adopted by research-ers for improvement of behavior of RAC. Tam et al.( 2007) conducted investigation on the properties of concrete designed by Two-stage mixing approach with RCA sub-stitution between 0% and 100% and reported that about 25–40% of RA substitution was found to be most suitable in using TSMA for achievement of optimum property. Fur-thermore, around 50–70% of RCA replacement could pro-vide some improvement in compressive strength although these enhancements of CS were not so significant as com-pared to that of 25–40%. Tam and Tam (2008) modified two Two-stage mixing approach and developed two meth-ods known as two-stage mixing approach (silica fume) (TSMAs) and two-stage mixing approach (silica fume and cement) (TSMAsc), which are modification of Two-stage mixing approach (TSMA). The TSMA was based on the procedure in which the total quantity of mixing water was divided into two parts. During the first stage of mixing, half of the required water was utilized for mixing leading to the development of a thin layer of cement slurry on the surface of RCA, which would permeate into the porous old cement mortar, filling up the old cracks and voids. At the second stage of mixing process, the residual water was added to complete the concrete mixing process. In TSMAs, silica fume was added by replacing 2% of the required cement into certain percentages of RCA in the pre-mix procedure and the residual natural aggregates, fine aggregates, the remaining cement and water were then added during the second mixing process. The other mixing technique TS-MAsc method was based on addition of silica fume and proportional amounts of cement into certain percentages of RCA in the first mix and then the remaining aggregates, cement and water were added during the second mixing process. Compressive strength of RAC produced with aforementioned methods enhanced as silica fume acts as reinforcing filler for the space inside RCA and porosity of old adhered mortar was reduced. Furthermore, SF reacts with Ca(OH2) and facilitates the acceleration of the hy-dration of tricalcium silicate (3CaO. SiO2) and dicalcium silicate (2CaO. SiO2). Improvement of tensile strength was also observed due to formation of a stronger ITZ. Li et al. (2009) used fly ash, silica fume, blast furnace slag



for production of improvement of RAC adopting a coating technique. It was concluded that combination of Portland cement, fly ash and silica fume was very effective in im-proving compressive strength RAC that was mainly attrib-uted to the development high packing density in concrete. Corinaldesi and Moriconi (2009) studied the effect of addi-tion of silica fume and fly ash on the behavior of concrete manufactured by completely replacing fine and coarse ag-gregates with recycled aggregates from a rubble recycling plant. The conclusion from the study was that addition of silica fume and fly ash improved the compressive strength of concrete.

Nanotechnology, one of most promising technology of last two decades has made it possible to develop new materi-als with new functions or improvements in the properties of existing materials using nanotechnology are new areas of interest in civil engineering. The application of nano-particles in cement based products is growing as these particles are very effective in filling the void spaces pres-ent in the C-H-S link, increasing the rate of hydrations and diminishing the size of Ca (OH)2 crystal (Pacheco-Torgal et al., 2010). Among existing nano-particles, Nano¬silica (NS) is quite influential nano-material to be applied in the field of cement and concrete for enhancing the properties of cementious products. NS was preferred in place of SF in cement based paste as the SF had higher of rate of consumption of Ca(OH)2 crystals and higher pozzolanic activity than SF at early days (Qing et al., 2007). NS was improved the mechanical properties and the microstruc-ture of high-strength cement pastes even in low concen-tration by improving packing among particles (Stefanidou and Papayiann, 2012). However, the incorporation of NS to paste and mortar affected the mix workability by reducing the amount of mixing water available intended for proving sufficient fluidity (Berra et al., 2012). The compressive and tensile strength of cement mortar containing NS are en-hanced due to the enhanced pozzolanic action and filling of the voids present in microstructure (Jo et al., 2007).

The colloidal form of NS was better than dry powder form from application point of view because it was more dis-persive in nature and segregation of nano-particles as compared to dry powder form of NS (Quercia et al., 2012). The application of NS in concrete had improved com-pressive strength (CS) and reduced porosity due to fact that the addition of NS led to significant consumption of portlandite (CH) in the pozzolanic reaction and removal of minute pores present in cement mortar matrix, hence making concrete strong and dense (Said et al., 2012). The addition of 3% of NS to fully RAC by replacing cement pro-duced CS more than that of concrete made with natural aggregates. Moreover, the microstructure of the concrete became dense, uniform and even extremely small voids had been omitted due to the filling effect of NS (Hosseini et al., 2011).

Design of Experiments (DOE) is a useful tool for system-atically investigation of the process or product variables

that influence product quality after identifying the process conditions and product components. As of the resources are limited, it is essential to collect the maximum informa-tion from each experiment that conducted. Furthermore, a well-designed experiment would ensure about the evalu-ation of the effects of significant factors (Montgomery, 2012). Determining the objectives of an experiment and selecting the process factor for study is the primary thing in DOE. An experimental detail Design is the laying out of a detailed experimental plan in advance of doing the experi-ment considering the all factors those affect the process. Taguchi Design, based on the DOE approach, is a robust parameter design methodology of product or process de-sign dealing with the minimization of variation s compared to factorial designs. Taguchi design adopts an Orthogonal Array system, which facilitates analyzing the effect of many factors with carrying out less number of experiments. As characteristics of RAC are dependent upon several fac-tors, huge numbers of experiments are required to under-stand the influence of the factors. Earlier works confirmed that Taguchi approach could be utilized in field of cement and concrete are available and some of those studies are discussed below.

Based on use of Taguchi Approach with Orthogonal Array and Analysis of Variance (ANOVA), the optimal mixture of concrete which would yield optimum slump and compres-sive strength was selected (Lin et al. 2004). Analysis of the results of slump and compressive strength of concrete in-dicated that the optimal alphanumeric series of designation of experiment was water/cement ratio of 0.5, volume ratio of coarse aggregate of 42.0%, 100% natural river sand, 0% crushed brick, and as-is recycled aggregate without water-washed aggregate. Taguchi method was utilized for deter-mination of quantity of materials required to achieve opti-mum physical properties such as porosity, capillarity, water absorption, unit-weight, and UPV that will yield to the most durable concrete mixtures (Turkmen et al., 2008). In this study, the factors considered for the experimental investi-gation were mineral admixture, water-to-binder ratio, curing regime and curing time. The study concluded that among all parameters, curing regime was most significance fac-tor, which affected capillarity coefficient, capillary porosity, UPV, and porosity. However, the water-to-binder ratio was the most influencing factor on the water absorption and dry-unit weight. The procedures of Taguchi method were followed for analyzing the effect of various mix design pa-rameters on the behavior of high strength self-compacting concrete (Ozbay et al., 2009). In this study, water/cementi-tious material ratio, water content, fine aggregate to total aggregate percent, fly ash content, air entraining agent content, and superplasticizer content were considered as factors and concrete mixtures were designed according to L18 orthogonal array. Compressive strength, splitting ten-sile strength, air content, water permeability, UPV, and wa-ter absorption were the responses, which were analyzed and for individual response optimum mix proportion was determined. Furthermore, Taguchi method was adopted



for optimization of the of fly ash geopolymer concrete mix-tures (Olivia and Nikraz, 2102). Properties of nine mixtures were analyzed by taking into consideration of the effects of factors such as aggregate content, alkaline solution to fly ash ratio, sodium silicate to sodium hydroxide ratio, and curing method. The findings of the study was that the mechanical properties of the geopolymer mixtures tested were competitive with those of OPC concrete and offer a more durable substitute to the OPC concrete in a seawater environment. Chang et al. (2011) adopted Weighted Grey Taguchi Method (Integration of Grey Relational Analysis of DOE and a weighting technique into Taguchi method.) which was the incorporation of weighting technique into Grey Taguchi Method to solve the optimal mixture problem having multiple responses. The analysis concluded that the optimal mixture of RAC was at water cement ratio of 0.5, volume ratio of recycled coarse aggregate of 42.0%, 100% replacement of river sand, 0% crushed brick, and water-washed aggregate. The investigations in the area of application of coarse recycled aggregates for production of concrete are often available in open literature. However, fewer studies have been carried out comprising of the use of NS in RAC. The characteristics of RAC is dependent of a large number of factors since there aggregates are pro-duced from waste concrete having unknown properties. Therefore, a large number of tests are generally required as to decide a suitable mixture for obtaining the desired requirements in view of variable engineering/mechanical properties of RCA and Nano-silica. For aforementioned reason, application of Taguchi method is one of the solu-tions that could reduce the number of experiments along with achievement of optimum working condition. However, the study comprising of application of Taguchi methodol-ogy in designing concrete mixes incorporating recycled aggregates and NS is not found in literature. Therefore, the aim of present investigation is to use Taguchi method for determining the influence of different factors on the prop-erties of RAC containing NS and to find out suitable mix proportions of concrete to produce optimum response. The objectives of the present study are follows:

• Preparation of RCA from the waste concrete collected • Characterizations of RCA collected from field source • Determination of properties of binding material • Assortment of factors and their levels • Determination of performance characteristics • Selection the suitable Orthogonal Array matrix Experi-

ment • Preparation of concrete mixtures and testing of speci-

mens • Analysis of the experimental results and Prediction the

Optimum Levels • Conducting verification experiment and comparison

study

Taguchi Analytical Methodology

Background In the traditional method for carrying out ex-

periments when the process is controlled by several fac-tors, is to keep one factor varying at a time, and all the other factors are kept constant. The optimum conditions achieved in the conventional approach of experimentation may not be accurate optimum result if the interactions be-tween the factors are significantly affecting the process. Full factorial experiments and response surface designs could be useful to analyze the effect of factors and their involved interactions. However, the number of experiments is quite large in the case of a full factorial design, and it is almost not possible to perform these required experiments in most of the cases due to lack of recourses. Therefore, the fractional factorial experiments are quite useful and fractional factorial experiments using orthogonal array was proposed by Taguchi.

The quality engineering method that Taguchi proposed is commonly known as the Taguchi Method or Taguchi Aproach, which is based on Design of Experiments (DOE) approach, is a powerful tool for the design of a high quality system with minimization of resources. Moreover, it pro-vides not only an efficient, but also a systematic procedure to optimize designs for achievement of better performance and quality than factorial designs. One of Taguchi’s tech-nical contributions to the field of quality control was a new approach to industrial experimentation. Taguchi offers a generalized definition for quality of performance regarding performance as the major component of product or pro-cess quality. The aim of Taguchi method is to find control factor settings that produce satisfactory responses in spite of process variability. Taguchi Process is based on orthog-onal array (OA) experiment (well defined minimum no. of experiment), gives much reduced variance of experiment with best level of control factors and also improves the ef-ficiency and effectiveness of DOE. In other words, Taguchi parameter design technique could able to optimize the performance of the system through the settings of design parameters and with reduction of the sensitivity of system performance to source of variation. Therefore, Taguchi Ap-proach achieves the merge of DOE with optimized control factors to obtain the best result. The Steps in Taguchi Pro-cess are follows:

• Problem Identification• Identification Control Factors and setting their Levels• Selection of the Orthogonal Array matrix Experiment• Run Experiment following Taguchi’s suggestion• Analysis of the experimental, Predict the Optimum Lev-

els• Perform Verification Experiment

Orthogonal arrays

Taguchi method establishes both the optimal result from limited number of experimental results and the significant factors involved of the system as compared to other opti-mal methods. Depending on the number of factors affect-ing the process and their levels, there are many possible



ways in which an experiment can be designed. A number of standard orthogonal arrays are available to facilitate ex-perimental design. Each of these arrays can be used to design experiments to suit several experimental situations. As the orthogonal arrays developed by Taguchi are frac-tional orthogonal designs, these designs could be used to estimate main effects of a process by conducting only a few experimental runs. The proper orthogonal array can be selected after determining the number of control factors and the number of levels. Using the array selector from the Table 1, the name of the appropriate array can be found by looking at the column and row corresponding to the number of parameters and number of levels. These arrays were created using an algorithm Taguchi developed, and allowed for each variable and setting to be tested equally.

Signals to Noise Ratio (S/N Ratio)

Taguchi method adopts the S/N ratio (signal-to-noise), which is known to be performance characteristic or inspec-tion index and it is expressed in (S/N unit: dB), rather than the mean value to interpret the experiment result data into a value for the evaluation characteristics in the optimum setting analysis. Moreover, this ratio indicates about the scatter or variation of results around a target value. Tagu-chi’s signal-to-noise ratios are functions of the observed responses over an outer array. Dividing system variables according to their signal and noise factors is a key ingredi-ent in robust Engineering. Signal factors are system control inputs. Noise factors are variables that are typically difficult or expensive to control. Depending upon the objective of the robust parameter design experiment, there are three categories of performance characteristics used in Taguchi method, the larger—the better, the smaller—the better and the nominal—the better. The formula for the performance statistics depends on the condition, whether the experi-mental goal is to maximize, minimize or match a target value of the quality characteristics of interest.

Smaller the Better (For making the system response as small as possible) Choose when the goal is to minimize the response.

(1)

Nominal the Best (For reducing variability around a target) choose when the goal is to target the response and it is required to base the S/N ratio on standard deviation only.

(2)

Larger the Better (For making the system response as large as possible) choose when the goal is to maximize the response.

(3)

Where y is the average of observed data, s2 the variation of y, n the number of observations, and

y the observed data. A larger value of signal-to-noise is considered preferable in this present investigation since the mechanical properties of concrete to be maximized. Analysis of Variance (ANOVA) of the results is performed for determination of the reliability of the experimental re-sults obtained by experimental plan following Taguchi or-thogonal array and the degree of the effect of the factors on these results. ANOVA is normally used to provide with a confidence level and consequently, this confidence is measured from the variance. Therefore, optimum condi-tions could be achieved according to the procedures of Taguchi method, and with controllable factors and fixed levels consisting of standard OA.

Experimental design and approach

Determination of the control parameters and levels

The first step in Taguchi’s statistical design is to select control factors or parameters and fix their levels. Based on the available literature and laboratory trials, the factors and their levels for mix designing concrete containing RCA and NS are chosen. In the present study, the following param-eters are considered for mix proportioning of concrete:

• Water-Cement Ratio i.e. W/C ratio

• Maximum Cement Content (Kg/m3)

• Replacement of Natural Coarse

• Aggregate with Recycled Coarse Aggregate (%) or Re-cycled Coarse Aggregate (%)

• Replacement of Cement with Nano-Silica (%) or Nano-Silica (%)

As per IS 10262-2009, the maximum Water Cement Ratio is 0.45 and minimum cement content is 310 Kg/m3 for M-

Table 1 Taguchi Orthogonal Array



30 grade of concrete. Previous studies recommend that the use of Nano¬silica should be within three to five per-centages to avoid adverse effects on workability. Based on study of previous researchers the levels of each control factors have been fixed and shown in Table 2.

The recycled coarse aggregates used in this experimen-tal work are collected from a demolished building of Jhar-gram, West Bengal. The large pieces of waste concrete, which are free from impurities, transported to the labora-tory and broken in to small pieces. The pieces greater than 20 mm are crushed by jaw crusher and are sieved through the required sieves in order to make it 20 mm well graded nominal size aggregate. The percentage of aggregates re-quired to pass in particular sieve size were segregated as per IS: 383-1970. Natural aggregates 20 mm well-graded nominal size aggregate are used for production of con-crete mixes. The natural river sand confirming to Zone II (IS: 383-1970) is used as fine aggregate. The standards tests for determination of physical and mechanical proper-ties of the aggregates have been conducted and results of those tests are tabulated in Table 6.

Colloidal Nano-silica (CNS) is having particles size 9-20 nm

Control Parameters Level1 Level 2 Level 3

A Water Cement Ratio (W/C) 0.39 0.42 0.45

BReplacement of Natural Coarse Ag-

gregate with RCA (%)0 50 100

C Maximum Cement Content ( Kg/m3) 350 400 450

DReplacement of Portland Slag Cement

with Nano-Silica (%)0 1.5 3

Table 2 Control Parameters and Levels

Selection of suitable Orthogonal Array

According to the factors and their variation levels presented in Table 2 and the suitable array from Table 1, orthogonal array is devised. In this present study, Considering all the four factors each having three levels a standard of L9(34) has selected using MINITAB 16 software, which represents 9 Runs 4 factors with three levels giving rise to a total nine combination trial mixes L9(34) orthogonal array (OA) is se-lected. The standard L9(34) OA is shown in Table 3.

Trial Factor A Factor B Factor C Factor D

1 1 1 1 1

2 1 2 2 2

3 1 3 3 3

4 2 1 2 3

5 2 2 3 1

6 2 3 1 2

7 3 1 3 2

8 3 2 1 3

9 3 3 2 1Table 3 Standard L9(34) orthogonal Array

Materials for different mixes are calculated according to the mix design procedure of IS 10262:2009. All the nine no of trial mixes are designed for M30 and the Water-cement ratio for different mixes is fixed at 0.39, 0.42 and 0.45 respectively; however depending upon the amount of recycled aggregates in a particular mix, the correction for water absorption is made. The percentage proportion is made by weight and the ratio is applied for each sieve size and not to the whole aggregate. Levels and L9(34) or-thogonal array, the mix proportions are defined as shown in Table 4 by using the selected parameters.

Materials

The cement used in this research is Portland Slag Cement is produced by inter grinding clinker, granulated blast fur-nace slag and gypsum or by blending ground slag with Portland cement. Standard test are conducted for determi-nation of properties of cement and presented in Table 5.

Mix No. W/C ratioRecycled Coarse Aggregate (%)

Maximum Cement Content

(Kg/m3)

Nano-Silica (%)

1 0.39 0 350 0.0

2 0.39 50 400 1.5

3 0.39 100 450 3.0

4 0.42 0 400 3.0

5 0.42 50 450 0.0

6 0.42 100 350 1.5

7 0.45 0 450 1.5

8 0.45 50 350 3.0

9 0.45 100 400 0.0Table 4 Details of mix concrete proportions

SpecificationPortland Slag Cement: Re-quirement of IS:455:1989

Test Results

Fineness(cm2/gm) 225 m2/kg 235 m2/kg

Setting Time (Minutes)

Initial 30 90

Final 600 300

Consistency 34%

Specific Gravity 3.15 3.02Table 5 Physical Properties of Portland Slag Cement

Property of AggregateNatural

Coarse Ag-gregate

Recycled Coarse Ag-

gregate

Natural Fine Aggregate

Specific Gravity 2.9 2.36 2.66

Water Absorption 0.5 4.6 0.2

Bulk Density (kg m-3)

Compacted 1870 1570 1560

Loose 1810 1160 -

Flakiness Index 23 12.04 -

Elongation Index 34 35.18 -

Crushing Value 24.67 34.5 -

Impact Value 26.53 36.57 -Table 6 Physical and Mechanical Properties of Coarse Aggregates



are used for the experimental work. CNS is small particles consisting of an amorphous SiO2 core with a hydroxylated surface, which are insoluble in water. The pozzolanic re-activity of Nano-silica is high due to high surface area and possesses unsaturated bonds. Nano-silica is having solid content 40% and density 1.2 gm/cc.

Preparation, casting and Testing of specimens

For production of concrete mixtures, the requisite amount of all dry materials such as coarse aggregate, fine aggre-gate and cement are weighted (by mass) and loaded in the concrete mixture and mixing of materials were done for one minute. As the Nano-silica is soluble in water, the required amount of NS is added to the water. The mixture of NS and water are added to the mixtures and mixing is done properly. After mixing of materials, the fresh concrete is poured in to the specific moulds and left for drying for 24 hours. Then, concrete specimens are removed from moulds after 24 hours and curing is done under water for required duration at normal temperature and humidity conditions. The water cured specimens are surfaced dried surface dried before testing. The compressive strength is determined on standard cubes of size 150 mm using 3000 KN compressive testing machine in accordance with BIS (IS: 516-1959). Elastic modulus of concrete mixes is de-termined using cylindrical specimens of 150 mm × 300 mm height according to the procedures given in BIS (IS: 516-1959). The split tensile strength test of concrete af-ter 28 days is performed on cylindrical specimens of 150 mm × 300 mm height using 3000 KN compression test-ing machine according to the procedure given in BIS (IS: 5816¬1999). The flexural tensile strength test is conducted on prisms of size 100×100×500 mm after 28 days curing. The test is done in accordance with BIS (IS: 516-1959) us-ing 100 KN universal testing machine.

4. Results and Discussion

In Table 7, the results of Compressive Strength (CS), Split Tensile Strength (STS), Flexural Tensile Strength (FTS) and Modulus of Elasticity are presented. Each of the results represents the average of experimental values of three specimens. The procedures of Taguchi method are followed

for analysis of experimental results and those are present-ed in following sections.

The variation of compressive strength of nine trial mixes at 7 and 28 days is presented in Table 7, which illustrates that the 7 and 28 Days compressive strength lies between 20-27 MPa and 29¬40 MPa respectively. Based on analysis of variance of test results, the significance of each factor on 7 days compressive strength is evaluated and the cor-responding S/N ratio at each level of the parameter has obtained by using ANOVA. The response value of S/N ratio of 7 days compressive strength at three different levels of the control factors are presented in Table 5.

Mix No.7 Days

CS (MPa)28 Days

CS (MPa)STS

(MPa)FTS

(MPa)Modulus of

Elasticity (GPa)

1 23.2 33.0 1.83 4.9 32.83

2 24.8 35.7 1.94 5.28 31.58

3 26.9 39.0 2.10 5.42 30.91

4 25.0 36.5 1.97 5.40 32.90

5 24.2 34.2 1.89 5.12 31.79

6 19.7 31.8 1.79 4.88 30.23

7 24.5 35.5 1.90 4.98 31.29

8 21.3 32.5 1.74 4.68 29.64

9 19.0 28.8 1.62 4.25 28.16

Table 7 Test Results of hardened Concrete 4.1. Compressive Strength

LevelFactor A: W/C Ratio

Factor B: RCA (%)

Factor C: Maximum Cement content(Kg/3)

Factor D: NS (%)

1 27.93 27.56 26.59 26.85

2 27.17 27.38 27.14 27.07

3 26.52 26.69 27.9 27.71

Delta 1.41 0.88 1.31 0.85

Rank 1 2 3 4

Table 8 Response Table for S/N Ratio of 7 days CS vs Control Factors

Fig. 1 shows the main effect plot of all the control param-eters at three different levels. Regardless the category of the performance characteristics, a greater S/N value cor-responds to a better performance. Therefore, the optimal level of the 7 Days compressive strength is the level with the greatest S/N value. The main effects plot for S/N ra-tios for the 7 days compressive strength considering all the factors is presented in Fig. 3, which indicates that the response 7 days CS improves with increases with increase in the factors maximum cement content and NS (%). This observed enhancement of strength with increase in addi-tion of NS is mainly because of densification of concrete with removal of voids present in concrete. Furthermore, the improvement of strength with increase in cement content is due to increase in binding material, which improves the bonding between paste and aggregates. However, 7 days CS reduces with increase in W/C ratio and RCA (%). The reduction in 7 days CS with increase in RCA (%) is due to the degradation of concrete quality with incorporation of recycled aggregates whose properties are inferior to vir-gin aggregates. Moreover, the reduction of 7 days CS with increase in W/C ratio is attributed the fact that increase in W/C ratio weakens the mortar matrix subsequently affect-ing the strength of concrete.

Table 9 shows S/N ratio values for the response of 28 days CS analyzed through ANOVA. Delta is the difference be-tween the maximum responses to the minimum response. Based on the analytical result the factor replacement of Nano-Silica is having rank one whereas replacement of RCA is having rank 4.

Based on the main effect plot for S/N ratio of 28 days CS presented in Fig. 2, the all the factors are significantly af-fecting the response 28 days CS. The optimal value of 28



days CS is achieved when water cement ratio is kept at 0.39 (level 1), replacement of RCA at 0% (level 2), Maxi-mum cement content at 450 kg/m3 (level 3), and replace-ment of Nano-silica at 3% (level 3) i.e. at A1B1C3D3.

Split Tensile Strength

Table 7 represents the of split tensile strength of nine num-bers of trial mixes at 28 days, which lies between 1.63-2.1 MPa. The experimental results of STS test are analyzed using ANOVA and the corresponding S/N ratios for values are listed in Table 10, which illustrates that Water cement ratio is at rank one followed by Nano-silica (%), Maximum cement content and replacement of RCA at rank 4.

Fig. 1. Main Effect Plot of 7 Days Compressive Strength


Factor B: RCA (%)


Factor D: NS (%)

1 31.08 30.87 30.22 30.08

2 30.66 30.66 30.49 30.07

3 30.14 30.35 31.17 31.10

Delta 0.94 0.52 0.95 1.03

Rank 3 4 2 1

Table 9 Response Table for S/N Ratio of 28 days Compressive Strength vs Control Factors

Fig. 2. Main Effect Plot of 28 Days Compressive Strength

Using the experimental value it is observed that in case of 7 days compressive strength the factor water cement ratio is at rank1 and NS (%) is at rank 4 whereas in case of 28 days compressive strength the replacement of NS (%) is at rank 1 and RCA (%) is at rank 4. However, it could be seen that the difference between the delta value for NS (%) and W/C ratio for 7 days CS not so significant, which indicate that contributation of NS (%) also significant although it is ranked 4 among all factors.


Factor B: RCA (%)


Factor D: NS (%)

1 4.453 3.776 3.488 3.438

2 4.088 3.592 3.619 3.486

3 2.387 3.560 3.821 4.003

Delta 2.067 0.216 0.333 0.565

Rank 1 4 3 2

Table 10 Response Table for S/N Ratio of Split Tensile Strength at 28 days vs Control Factors

From the main effect plot shown in Fig. 3 for S/N ratio of split tensile strength the optimal performance is at water cement ratio of 0.39 (level 1), replacement of RCA at 0% (level1), Maximum cement content at 450 kg/m3(level 3) and replacement of Nano-silica at 3% (level 3) i.e. at A1B1C3D3.

Fig. 3. Main Effect Plot of Split Tensile Strength

Flexural Tensile Strength

Table 7 represents the experimental value of flexural tensile strength for nine numbers of trial mixes. The measured ex-perimental data are analyzed statistically and correspond-ing S/N ratio values are listed in Table 11. Water cement ratio is at rank one, followed by of NS (%), Maximum ce-ment content and RCA (%) at rank four.

Fig. 4 shows the main effect plot for S/N ratio of Flexural Strength at 28 days, which is maintaining similar in trend as split tensile strength. From the main effect plot for S/N ratio of flexural strength the optimal performance is at wa-ter cement ratio of 0.39 (level 1), replacement of RCA at



0% (level1), Maximum cement content at 450 kg/m3(level 3) and replacement of Nano-silica at 3% (level 3) i.e. at A1B1C3D3.

mum cement content as 450 Kg/m3 , water cement ratio 0.39, and 3% NS, and three different percentages of RCA (0%, 50% and 100%). The selected mix proportions are shown below.

• Mix no. I: W/C ratio-0.39, RCA-0%, Cement Content-450 Kg/m3, NS-3%

• Mix no. II: W/C ratio-0.39, RCA-50%, Cement Content-450 Kg/m3, NS-3%

• Mix no. III: W/C ratio -0.39, RCA-100%, Cement Con-tent-450 Kg/m3, NS-3%


Factor B: RCA (%)


Factor D: NS (%)

1 14.30 14.13 13.66 13.52

2 14.20 14.0 13.87 14.04

3 13.31 13.67 14.27 14.24

Delta 0.99 0.46 0.61 0.73

Rank 1 4 3 2

Table 11 Response Table for S/N Ratio of Flexural Strength at 28 days vs Control Factors

Modulus of Elasticity

Table 7 shows the results of the Modulus of Elasticity (E) test of all nine numbers of trial mixes. The response data are measured from the experiments and their correspond-ing S/N ratio values are in Table 12. The factor RCA (%) is at rank one then followed by water cement ratio, Maximum cement content and NS (%) at rank 4. This type behavior could be attributed to the fact that Modulus of Elasticity of concrete is dependent upon the stiffness of aggregate and addition of pozzolanic materials have no effect on it. More-over, the optimal performance is at water cement ratio of 0.39 (level 1), replacement of RCA at 0% (level1), Maximum cement content at 450 kg/m3(level 3) and replacement of Nano-silica at 3% (level 3) i.e. at A1B1C3D3.

Fig. 4. Main Effect Plot of Flexural Strength

From the main effect plot of FTS shown in Fig.5, it is ob-served that the factors are significantly affecting the modu-lus of elasticity of concrete.

Validation of Experiments

From the above analysis, it could be concluded that Nano-silica (%) and water-cement ratio are the effective factors in most of the cases. To study behavior of recycled ag-gregate concrete, concrete mixes are produced with maxi-


Factor B: RCA (%)


Factor D: NS (%)

1 30.04 30.19 29.79 29.79

2 30.00 29.82 29.77 29.84

3 29.45 29.47 29.92 29.86

Delta 0.59 0.72 0.14 0.07

Rank 2 1 2 4

Table 12 Response Table for S/N Ratio of Modulus of Elasticity at 28 days vs Control Factors

Experiments for aforementioned three-trial mixes are con-ducted and the experimental results obtained. The ex-perimental results are interpreted and those are judged against the predicted results obtained by Taguchi Analy-sis. In Fig. 5 (a and b) comparative study of CS at 7 and 28 days and EM are presented, which illustrates that the values predicted results are nearer to experimental values and errors are within permissible limits.

Similarly, tensile strength results predicted by Taguchi method and experimental values are shown in Figs. 6 (a and b). It is observed that experimental results are close to predicted values, which provides confirmation about the precision of the method.

Fig. 5. Main Effect Plot of Modulus of Elasticity

Conclusion

In the present study, the influences of different factors on properties of RAC were investigated using Taguchi meth-od. It is concluded from the analysis of results that the fac-tors W/C ratio, maximum cement content, RCA (%), and NS (%) significantly influencing the responses. Statistical analysis of 7 days CS indicates that all the selected factors are significantly affecting the test results and W/C ratio is



being the most determinant factor. Similarly, analysis of 28 days CS depicts that NS (%) is the most significant factor among all factors. Analysis of the split tensile strength re-sults indicates that the effect of control factor W/C ratio is ranked one and then NS (%) is ranked two which suggests that W/C ratio and NS (%) have more influence factors compared to other two factors. Similar type of observa-tion is also found in case of flexural strength results. How-ever, the factor that affects the modulus of elasticity most is found to be RCA (%). Moreover, the comparative study of the predicted and experimental values concludes that for the optimum mix and experimental value demonstrates that the error is within the permissible limits.

Author Affiliation

Prusty R1, Mukharjee B.B2, Barai S.V3

1Former Post-graduate student, Department of Civil Engineering, Indian Institute of Technology Kharagpur, India2Research Scholar, Department of Civil Engineering, Indian Institute of Technology Kharagpur, India3Professor, Department of Civil Engineering, Indian Institute of Technology Kharagpur, India

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The Class Theta Tensegrity Systems and Structures Based on Tetrahedron and Triangular Prism

Zbigniew Bieniek

Abstract

The relationship between forms and forces is one of the main topics o structural morphology. This harmonious co-existing relationship is very strong for systems in tensegrity state, currently called tensegrity systems.

It is currently apparent that among the tensegrity systems also exist cable-bar cells with a discontinuous network of cables. It is possible to design a separate set of cables inside the cable-bar elementary cell and to establish a self-stress state of equilibrium. In this connection, the au-thor of paper suggested to assume a new Class Theta tensegrity systems. Each of the basic tensegrity systems termed Class Theta possesses an external and internal set of tension components. The shape of Greek capital letter

(Theta) reflects two sets of such components (two sets of tendons, cables etc.). This notation corresponds to Skel-ton’s Class k tensegrity structure.

As shown in this paper, the Class Theta tensegrity cell can exemplify a geometrically and practically useful form for the lightweight and long-span modular structures; mainly but not only in view of civil engineering.

Key words: bar, cable, geometry, grid, module, prism, tet-rahedron, tensegrity

Introduction

Tensegrity systems are constructed by weak and gener-ally more numerous members (cables) that are flexible in unstressed state, together with strong and local members (bars); but they exhibit sufficient capability of resisting ex-ternal loads while suitably prestressed. Even when a mod-erate deforming force is applied at one point of the system, only a transient change is effected in the global form, after which the system once again returns to its equilibrium con-figuration.

The particular feature of so called ‘pure’ tensegrity is that bars are never connected to each other, while cables con-stitute a connected set as shown in Fig. 1. This is only one of possible choice of tensegrity systems. Tensegrity is now applicable to architecture as an established structural sys-tem, while it can be applied to other fields as well [1-3,7].

The problem of form-finding is central in the study of tensegrity systems [6]. The first attempts to create new elementary cells, that is the model tensegrity configura-tions called systems, were based on some simple char-acteristics. Tensegrity systems, and generally speaking - tensegrity structures, are based on the combination of a few simple but subtle and deep design patterns:

a)

b) c)

d) e)

Figure 1. Some examples of the ‘pure’ tensegrity systems in which the cables constitute a connected set.


• loading elements remain only in pure tension(in the case of cables) or pure compression(in the case of bars), meaning the structure will only fail if the cables yield or the bars buckle

• the prestress, or the preload in other words, which al-lows cables to be rigid in tension

• mechanical stability, which allows the elements to re-main in tension or compression as stress on the sys-tem increases.

Thanks to these patterns, no structural element experi-ences a bending moment. This can produce exceptionally rigid structures for their mass and for the cross section of the members.

These structures have another unique property. They can be either flexible/soft or rigid. When the tensegrity struc-ture needs to be rigid and sustain external loads, they can be activated at their required position. When the structure needs to be flexible, at least one of the members can be loosened causing the structure to evolve into a soft con-figuration susceptible to deformations. A flexible tensegrity necessarily has a smooth motion that is not a rigid motion of the whole tensegrity structure.

The Class Theta Tensegrity System

It is currently apparent that among the tensegrity systems also exist cable-bar cells with a discontinuous network of cables. It is possible to design a separate set of cables inside the tensegrity elementary cell and to establish a self-stress state of equilibrium [5,8,9]. In this connection, the author of paper suggested to assume a new Class Theta tensegrity systems. Each of the basic tensegrity systems termed Class Theta possesses an external and internal set of tension components. The shape of Greek capital let-ter (Theta) reflects two sets of such components (two sets of tendons, cables etc.). This notation corresponds to Skelton’s Class k tensegrity structure [4].

For example Fig. 2a shows the simplest Class Theta tensegrity structure, composed of four bars and ten cables in tension. We can to see, that the one set of four cables is located inside the other tetrahedral cable network. More-

over, both cable components are separable and interact with a discontinuous set of compressive members to form a stable cable-bar unit in space. In this way we can to build another the Class ‘pure’ tensegrity units. Among examples is a triangular prism shown in Fig.2b. We can to modify an external shape of the ‘pure’ tensegrity units by expansion of the internal set of tension and compression components.

Class Theta ‘Pure‘ Tensegrity Tetrahedron

There are a large number of possible topologies (node connectivities) with which tensegrity structures can be built. We restrict this part of paper to a particular minimal form of the Class Theta ‘pure’ tensegrity cell (thus =1, and present notation corresponds to Skelton’s Class k =1 tensegrity structure); in which three cables and one bar meet at each exterior node, as well as, two cables and one bar meet at each interior node. This tetrahedral tenseg-rity system with the connectivity depicted in Fig.3d has six exterior cables, and four interior cables and four bars. In-triguing characteristics of such a tetrahedron include the fact that it transforms from a compact bundle of bars into a full three-dimensional framework as the last cable (either exterior or interior) is pulled in tension, that it is form-finding structure. The cable-bar structure becomes a prestressed system.

From an engineering perspective, the class =1 tenseg-rity also possesses unique properties which we note at the outset.

The outward appearance of tetrahedral tensegrity cell is based on the space-filling tetrahedron called T2, as shown in Fig. 4, and interest readers may consult [10]. This solid is in fact Sommerville’s type II tetrahedron.

The tetrahedral tensegrity cell, in other words the tenseg-rity module, is also a space-filling structure that can be re-peated indefinitely by adding module after module in all directions.

The symmetry properties of the tetrahedral module can be easy in use during any estimations and precision structural analysis. a)

b)

Figure 2. Some examples of the Class tensegrity systems with separable bars; i.e. ‘pure’ systems: a) a tetrahedron, b) a triangular prism. The perspec-tive view of structure and the mother configuration of internal connections.



To begin with, there are two configurations of four bars in-side the tetrahedral cell: the counter-clockwise configura-tion and its mirror image – the clockwise configuration. It is shown in Fig. 5.

And second, each of configurations possesses three two-fold axes of symmetry. Furthermore, the axes are mutually perpendicular to one another and characteristic of whole tetrahedral module. This feature is shown in Fig. 6.

a) b)

c) d)

Figure 3. Possible topologies of the tensegrity tetrahedron: a) by Fuller (Class k =4), b) by Motro (Class k =2), c) the Class =2 tetrahedral cell, d) the Class =1 tetrahedral cell is the evident example of ‘pure’ tensegrity.

Figure 4. All the basic components of the Class =1 space-filling tetrahedral cell.

Figure 5. An enantiomorphism of the Class =1 tetrahedral cell: a) the sinis-trorse layout of bars, b) the dextrorse layout of bars.

a) b)

c) d)

Figure 6. Symmetry of the tetrahedral module: a) the perspective view of struc-ture and its two-fold axes, b-d) three axes of symmetry in the top view

a) b) c)

Figure 7. A pictorial diagrams of the equilibrium of internal forces for any node of the tetrahedral module: a) the perspective view of structure, b) a spatial concurrent force system in the external node, c) a coplanar concurrent force system in the internal node.

Fig. 7 exemplifies a self-stress state of equilibrium. Each element of the intricate cable-bar structure must be in a stable self-equilibrium.

Figure 8. A previous configuration and coplanar configuration.

a) b)



The tensegrity module shown in Fig. 8b is an example of coplanar configuration, in which an internal nodes occupy the appropriate faces of tetrahedral cell. It is worth to stress that the symmetry of tetrahedral module and the outside measurements stayed the same. The length of bars and internal cables suitably rose.

jointed together in many directions and by several meth-ods.

An expressive examples of the connecting of class theta tetrahedral tensegrity modules by face to face and edge to edge methods are shown in Fig. 11-13.

Figure 9. A coplanar configuration and example of expanded configuration.

As shown in Fig. 9, is hypothetical possible to build up the coplanar configuration toward a few expanded configura-tions.

A commentary:

In similar way we can to build another the Class ‘pure’ tensegrity units. Among examples is an internal structure of tensegrity tetrahedron shown in Fig. 10.

a) b)

c) d)

Figure 10. An examples of modification of an internal structure of the Class tensegrity tetrahedron with separable bars: a) the perspective view of structure, b) the tetrahedral configuration of internal connections, b’) the tetrahedral expanded configuration of internal connections, c) example of the system reinforced by four additional cables[5,11].

Class Theta Modular Girders and Grids

The tensegrity girders and grids can be composed of the same tetrahedral tensegrity modules and subsequently

a)

b)

c)

d)



Class Theta ‘Pure‘ Tensegrity Triangular Prism

It is possible to insert a separate set of cables inside the cable-bar prismatic cell and to establish a self-stress state of equilibrium.

At present, the outward appearance of the mother Class Theta tensegrity module is based on the triangular prism. A physical model of this module is shown in Fig. 14. The identical topology of a physical model in expanded con-figuration we can to show in Fig. 15. However, is visible a definitely different geometry of both modules.

e)

f)

Figure 11. Some variants of the linkage: a-e) an examples, f) the angle signed α depends on established length of bars and ‘internal’ cables.

Figure 12. Some variants of the modular tensegrity girders.

a)

b) c)

Figure 13. Modular tensegrity grids. In grid from Fig. 13b-c can be use only the bars instead of visible cables and remaining structural members. And thus, we obtain an intriguing forms of planar and space trusses.

Figure 14. Front view and top view of the physical model in the mother con-figuration.



Geometrical Behaviours

There are two configurations of six bars inside the module: the counter-clockwise configuration and its mirror image – the clockwise configuration. It is shown in Fig. 16.

Examples of Multistage Towers and Planar Grids

Both the Class ‘pure’ tensegrity triangular prism in the mother configuration and expanded configuration can to exemplify the structural module of towers, girders, grids and more complex spatial tensegrity structures. Some examples of various geometrical solutions for lightweight cable-bar structures are shown in Fig. 20-27.

According to the method applied in all examples for tensegrity towers and which is called ‘face to face’, adjoin-ing each other units are connected in the linear self-rigid cable-bar structure. More rigid structures can be obtained with the help of the additional core cables attached to the appropriate internal nodes, see Fig. 20b and Fig. 20b’.

Figure 15. Front view and top view of the physical model in the expanded configuration.

Figure 16. An enantiomorphism of the Class =1 prismatic cell: a) the sinistrorse layout of bars, b) the dextrorse layout of bars.

a) b)

a) b)

Figure 17. Symmetry of the Class =1 prismatic cell: a) the perspective view of cables(on left) and all structure(on right) and one three-fold axis of symme-try, b) three two-fold axes of symmetry in the perspective and top views.

Each configuration possesses one three-fold and three two-fold axes of symmetry. This feature is shown in Fig. 17 and Fig. 18. The traits of symmetry are identical in case of the expanded configuration shown in Fig. 19 and Fig. 15 previously.

a) b)

Figure 18. Symmetry of the Class =1 prismatic cell; the view in direction of optional two-fold axis of revolution.

a) b)

Figure 19. The Class tensegrity triangular prism in expanded configuration: a) perspective view, b) front view and top view.

Figure 20. An examples of modular tensegrity tower erected by ‘face to face’ linkage: a’) and b’) composed of identical tensegrity modules, a) and b) every other module is a mirror image of the previous module, b) and b’) represent the towers reinforced by the additional core cables(in yellow).

a) a’) b) b’)



Both geometry of the triangular prism like module and ge-ometry of the modular tower and tension in all cables is easy to maintain, to change or to reinforce, by shortening only the core cables.

Figure 21. Example of modular tensegrity grid erected by ‘edge to edge’ link-age. The pattern is based on the expanded configuration of mother module.

Figure 22. The pattern of common cables in the modular tensegrity grid, perspective and top views respectively.

Figure 23. The planar triplet by ‘edge to edge’ linkage in a perspective view.

Figure 24. The Class Theta reinforced tensegrity grid: a) the planar triplet by ‘edge to edge’ linkage in a perspective view completed with the additional cables of top(in blue and dashed lines) and bottom(in red and dashed lines) layersb) the layout of more complex planar tensegrity grid made of the prismatic modules in expanded configuration and reinforced by two sets of the ad-ditional cables(marked by blue and red dashed lines).

a) b)

Under similar circumstances can to erect the modular tensegrity towers with the help of the expanded configura-tion of mother module.

The simple version of planar tensegrity grid erected by ‘edge to edge’ linkage is shown in Fig. 21. This one was composed of the expanded tensegrity modules. The pat-tern of common cables and perspective view for this modular triplet we can to see in Fig. 22 and Fig. 23 re-spectively.

The Class Theta reinforced tensegrity grid made of the same ‘pure’ tensegrity prismatic modules in expanded configuration is shown in Fig. 24. However, the pattern lay-out of a basic and additional cables we can to see in Fig. 25. By skilful shortening only the additional cables is pos-sible to maintain or to reinforce of the structural rigidity of a such modular tensegrity grids.

The next modular tensegrity design represents an another geometrical solution of the planar grid based on the Class Theta ‘pure’ tensegrity triangular prism in expanded con-figuration. This time, the mirror pairs of basic module are jointed together forming a very original pattern of the pla-nar reinforced grid as shown in Fig. 26 and Fig. 27.

Figure 25. The planar pattern of a basic and additional cables in the modular tensegrity grid from Fig. 24.

Figure 26. The other version of the Class Theta reinforced tensegrity grid:

a) the planar four-cell complex made by ‘edge to edge’ linkage in a vertical view, completed with the additional cables of top(in blue and dashed lines) and bottom(in red and dashed lines) layers

b) the layout of more complex planar tensegrity grid made of the mirror pairs of prismatic module in expanded configuration, and then reinforced by two sets of the additional cables(marked by blue and red dashed lines).

a) b)



Final Remarks

Fundamental observations concerning geometrical char-acteristics of the Class Theta tensegrity systems ( = 1).

• A discontinuous network of cables

• the length of bars are significantly smaller in compari-son with the longest cables. ( in case of tensegrity sys-tems with k = 1, this family characteristic is contrary to

= 1)

• the system’s outer shapes can be completely different even though the topology of connections is identical.

Moreover, still current are the classic properties of tenseg-rity systems:

• an isolated bars in compression are situated inside a net of cables, in such a way that the compressed members(bars) do not touch each other and the pre-stressed tensioned members(cables) delineate the system spatially

• loading members are only subject to the pure compres-sion or pure tension, meaning the structure will only fail if the cables yield or the bars buckle

• preload or tensional prestress allows a cables to be rigid in tension

• no structural member experiences a bending moment.

Figure 27. The planar pattern of a basic and additional cables in the modular tensegrity grid from Fig. 26.

Author Affiliation

Zbigniew Bieniek

Faculty of Civil and Environmental Engineering Rzeszów University of Technology ul. Poznańska 2, 35-959 Rzeszów, Poland

References

1 Fuller R.B.: Synergetics: Explorations in the Geom-etry of Thinking, New York: Mac Millan Publishing Co. Inc.,1975

2 Snelson K.: Continuous tension, discontinuous com-pression structures, U.S. Patent No. 3,169,611, Febru-ary 11, 1965

3 Pugh A.: “An Introduction to Tensegrity”, University of California Press, Berkeley and Los Angeles, California, 1976

4 Skelton R.E., Helton J.W., Adhikari R., Pinaud J.P., Chan W.: An Introduction to the Mechanics of Tensegrity Structures, Dynamics and Control of Aerospace Sys-tems, University of California, San Diego, CRC Press LLC, 2002

5 Bieniek Z.: Chosen Ideas Of Geometrical Shaping Of Modular Tensegrity Structures, Structual Engineers World Congress, Como, Italy, 2011

6 Tibert A.G. and Pellegrino S.: Review of Form-Finding Methods for Tensegrity Structures, International Journal of Space Structures, 18:4, pp. 209-223, 2003

7 Motro R.: Tensegrity Structures, Fifty Years of Prog-ress for Shell and Spatial Structures, Mungan I., Abel J.F.(Editors), pp. 251-262, 2011

8 Bieniek Z.: Tensegrity - integrujące rozciąganie w sys-temach architektonicznych, Oficyna Wydawnicza PRz, Rzeszów,(in Polish), 2012

9 Bieniek Z.: Class Theta – a new kind of tensegrity sys-tems, Beyond the limits of man, IASS Symposium, Wrocław, 2013, on CD

10 Bieniek Z.: Space-filling tetrahedra, Symmetry: Art and Science, The Journal of the International Society for the Interdisciplinary Study of Symmetry (ISIS-Symmetry), pp. 44-47, 2009

11 Bieniek Z.: A review of the Tensegrity Systems, Sym-metry: Art and Science, The Journal of the International Society for the Interdisciplinary Study of Symmetry (ISIS-Symmetry), pp. 48-51, 2009



Study on Size Effect of RC and Rehabilitated Beam - Column Connections under Cyclic Loading

Marthong C1, Dutta A2*, Deb S.K2

Abstract

Beam-column connection is one of the vital structural parts, whose behaviour during earthquake is very critical. After an earthquake, connections may suffer damages and depending on the overall level of structural integrity, the re-habilitation can be carried out as appropriate. It is known that the size of the specimen plays a role in the evaluation of various properties related to seismic capacity. Thus, it was felt necessary to explore the possibility of existence of size effect in RC beam-column connections before and after rehabilitations. An experimental programme was un-dertaken by considering three types of RC beam-column connections and tested under displacement controlled cy-clic loading. Further, three different sizes of geometrically similar specimens were considered in each type and the studies were repeated on all the rehabilitated specimens. It was observed that the experimental results corroborated closely the size effect law proposed by Bažant in all the cases studied. In addition, it was also observed that the size effect became more prominent with the increase in brittleness of specimens. Further, a parameter, energy dis-sipation per unit volume ( ) was introduced and correlated with drift angles for different sizes of specimen. The varia-tion of stress with relative deflection was also studied for various sizes of the specimens. It was observed that en-ergy dissipation of specimens per unit volume of the D-region as well as variation of stress with relative deflection also followed the size effect principle.

Introduction

In classical theories such as elastic analysis with allowable stress or plastic limit analysis, existence of size-effect is generally not considered. Hence, material properties like tensile or compressive strengths measured by testing stan-dard laboratory samples of the material are usually used in all the engineering practices. However, it may happen that the size of the actual structural elements is different from those of the test samples. Many researchers conducted tests to evaluate the behaviour of rehabilitated RC beam-column connections under cyclic loading without varying the sizes of tested specimens [1-6]. Some tests results are available for scaled models for a particular deficiency [3, 7]. These results are unlikely to reflect the behaviour of full

size specimens as the size of the specimen plays an im-portant role in the evaluation of various properties related to seismic capacity. Available theories of material behavior that predict size effects are receiving increasing attention in the technical literature, where it has been demonstrated that the size of the specimen plays an important role.

Experimental study of size effect was primarily done for RC columns and beams [8-10]. Beam-column connections which are vital structural elements and play a very crucial role during earthquake needs attention. Size effect study of beam-column connections with and without retrofitting has been carried out by Choudhury [11]. It was shown that the size of the specimen played an important role in the evalu-ated properties like ultimate strength, energy dissipation etc. Thus, it was felt necessary to explore the possibility of existence of size effect on RC beam-column connections before and after rehabilitations.

In this experimental programme the behaviour of RC beam-column connections have been assessed by study-ing the performance of beam-column connections sub-jected to cyclic loading. Three common types of deficien-cies in RC beam-column connections were considered namely (a) Beam-column connections with beam weak in flexure (BWF), (b) Beam-column connections with beam weak in shear (BWS) and (c) Beam-column connections with column weak in shear (CWS). In each type, three geo-metrically similar specimens: full, two third and one third scaled sizes were considered. Further, in order to explore the effect of loading type, two types of loading were con-sidered in the test program. The different loading types considered in the test program were having different num-bers of cycles for a particular displacement. The control specimens with different deficiencies and tested under dif-ferent loading types experienced different extent of dam-ages. Hence, depending on the extent of damages, the damaged control specimens were rehabilitated by adopt-ing two rehabilitation strategies. The main objective of this research initiative were: (1) to carry out experimental studies on various types and sizes of deficient RC exter-nal beam-column connections under cyclic loading (2) to carry out experimental studies on the corresponding reha-bilitated specimens and (3) to interpret the experimental findings for exploring the existence of size effect in term of


various parameters like strength, energy dissipation, rela-tive deflection for both control as well as rehabilitated RC beam-column connections.

Experimental Program

Selection of the full scale specimen

The study was concentrated on an external isolated beam-column sub-assemblage as shown in Fig.1. It comprised of half the length of column on each side of the joint and part of the beam up to mid-span, which corresponded to the points of contra flexure in beam and column under lat-eral loads. As shown in Fig.1, N is the internal axial force of the column, P is the beam-tip load corresponding to the beam shear force, Vcol is the column shear force and Δ is the vertical beam-tip displacement. Symmetric boundary conditions were maintained at both the ends of column for isolation of a single unit of beam-column connections. In this study, a typical full scale residential building with floor to floor height as 3.3 metres and the beam of 3.0 metres effective span was considered.

mens, which is concrete in this case. For example, BWFLC stands for beam weak in flexure large concrete specimen; similarly CWSSC stands for column weak in shear small concrete specimens. All the eighteen control specimens were tested under cyclic displacement and the damaged specimens were rehabilitated appropriately. The rehabili-tated specimens were also named in line with the control specimens, e.g. BWFLRe meaning beam weak in flexure large rehabilitated specimen.

The specimens BWF were designed as under-reinforced beam following the provisions of IS: 456 [12], IS: 1893 [13] and IS: 13920 [14] for design and detailing. The speci-mens BWS were exactly similar in all respect to that of beam weak in flexure specimens, except the shear rein-forcement in beams. However, CWS specimens were cast by comparatively weaker grade of concrete than those used in earlier cases in order to make the column weak in shear. The cross section of the column was reduced while the cross section of beam was increased as compared to CWF and CWS. The main reinforcements in column were maintained similar to those of previous two cases, while same was increased in beam. Spacing for the lat-eral ties in the columns was increased to ensure the shear weakness of these specimens in column. The concrete mix used for beam-column connection with beam weak in flexure and beam-column connection with beam weak in shear was of target strength 30 N/mm2, while the mix for beam-column connection with column weak in shear was of target strength 25 N/mm2. Reinforcing steel of diam-eters 20 mm, 12 mm and 8 mm were of High Yield Steel Deformed (HYSD, Fe 500) bar type, while reinforcing steel of diameters 6 mm, 4 mm and 2 mm were of mild steel (Fe 250 ) type. The details of these specimens are shown in Fig. 2. The detailed descriptions of all the specimens are given in Table 1.

Fig. 1 Isolated exterior beam-column connection

Description of the specimens

In the present study, three types of specimens, namely, (a) Beam-column connection with beam weak in flexure, (b) Beam-column connection with beam weak in shear and (c) Beam-column connection with column weak in shear were considered. In each type, three geometri-cally similar specimens: full scaled, two third scaled and one third scaled sizes were considered. Two numbers of specimens were considered under each case and hence eighteen control specimens were considered in all for the study. All the three dimensions of two third and one third scaled specimens were arrived at by geometrically scal-ing down the dimensions of full size specimen. Similarly, reinforcement and coarse aggregates were also geometri-cally scaled down for satisfying the similitude requirement. The naming of the specimens was done with five alpha-bets, the first three alphabets cover the deficiency type, the fourth for size and the fifth for material type of speci-

(c) Fig. 2 Reinforcement details of beam-column connections: control specimens

(a) BWFLC (b) BWSLC and (c) CWSLC

(a) (b)


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Test set-up and instrumentations

The testing arrangement of specimens is shown in Fig. 3. Application of the load was facilitated by Strong floor, Strong wall and A-frames available in the Dynamic structur-al Testing Facility at IIT Guwahati. Servo hydraulic dynamic actuators (Make: MTS, USA) of capacity 250 kN having a maximum displacement range of 125mm was used. The column of the connection was placed in horizontal posi-tion while the beam was placed in vertical position in the set-up. An axial load of 10% of gross capacity of column was applied to the column to represent gravity load. To simulate the support condition at both ends of the column, roller supports were fabricated by making grooves inside mild steel plates. The MTS actuator was equipped with in-ternal load cell and linear-variable differential transformer (LVDT) for measuring actuator force and displacement re-spectively.

were increased after completion of three cycles under loading type-1, while only one cycle was used for each amplitude under loading type-2.

In order to utilize results obtained from cyclic loading test on structural elements for a general performance evalua-tion, there is a need to establish loading history that cap-tures the critical issues of the element capacity as well as the seismic demand. In the adopted loading type-2, em-phasis was given on the large inelastic excursion since they caused large damage and could lead quickly to ulti-mate state. Thus in order to draw conclusions for the ulti-mate states, a loading program with constantly increasing displacement was chosen. Further, it is recognized that structures depend on a large number of variables and a unique loading history will always be a compromise. Thus, in order to address the same, multi-cycle loading history (loading type-1) was also adopted in the presented work.

The typical displacement histories of both the loading types are shown in Fig. 4. The experiment for control specimens was stopped at a stage when the load came down in the range of 60-70 % of the ultimate load carrying capacity. All rehabilitated specimens were also tested with the same loading sequences as those imposed on the control speci-mens.

Specimen Beam Column

Span (mm) Section (mm) Longitudinal Reinforcement Length (mm) Section (mm) Longitudinal Reinforcement

BWFLC & *BWSLC 1500 300x360 2-20 -top 2-20 -bottom 3300 300x300 4-20 -total

BWFMC & *BWSMC 1000 200x2402-12 +1-8 -top

2-12 +1-8 -bottom2200 200x200 4-12 +2-8 -total

BWFSC & *BWSSC 500 100x1201-8 +2-6 -top

1-8 +2-6 -bottom1100 100x100 2-8 +4-6 -total

CWSLC 1500 240x450 3-20 -top 3-20 -bottom 3300 240x300 4-20 -total

CWSMC 1000 160x3003-12 +1-8 -top

3-12 +1-8 -bottom2200 160x200 4-12 +2-8 -total

CWSSC 500 80x150 2-8 -top 2-8 -bottom 1100 80x100 2-8 +4-6 -total

*Beam weak in shear specimens have same dimensions and longitudinal reinforcement as that of beam weak in flexure specimens except the shear reinforcement provided in beam.Table 1 Descriptions of beam-column connections

Fig. 3 Test set up

Loading Characteristics

The nature and extent of damage in a structure during earthquake depends on the characteristic of loading. Number of cycle in the displacement time history, frequen-cy of excitation and the level of displacement amplitude are some of the parameters which contributes to the ex-tent of damage in a specimen. In this study, test programs were divided based on two loading types. A displacement controlled mode with a loading frequency of 0.025 Hz was applied to the specimens. The displacement amplitudes

Fig. 4 Typical displacement history (a) Loading type-1 and (b) Loading type-2

Rehabilitation materials

A low viscous epoxy resin [Conbextra EP10 (base and hardener)] was used for injection into cracks. Micro con-crete (Renderoc RG) was used as a replacement mate-rial. Bonding agent (Nitobond EP) was used for bonding old and fresh added concrete and Nitocote VF was used for sealing cracks. All these materials were procured from


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Fosroc Chemicals (India) Pvt. Ltd.. Further, an injection pump (hand operated) and injection packer manufactured by WEBAC Chemie GmbH (Germany) were used for inject-ing epoxy into the cracked zone.

Rehabilitation strategies

The repairing strategy was aimed to retrieve back the lost capacity of the damaged connections to their respective original seismic capacity. Two rehabilitation strategies were employed depending on the degree of damages. These were Method-1: partial replacement of loose con-crete on the damaged area by micro concrete followed by epoxy injection into crack zone and Method-2: complete replacement of crushed concrete on the damaged area by micro concrete followed by epoxy injection into crack zone. The voids created after removal of loose materials were patched or filled with micro concrete after a suitable bonding agent was applied on the clean surface for attain-ing adequate bond between old and freshly added con-crete. Holes were drilled along cracks and packers were inserted through these holes, which served as filler neck for epoxy injection. Visible cracks were sealed and a low viscous epoxy resin was injected under high pressure into the cracked zone. Once the injected epoxy resin attained sufficient strength, the installed packers were removed by striking its head and a grinding machine was subsequently

used to remove the sealing materials. Fig. 5 and 6 illus-trates various steps of repair operations for typical dam-aged beam-column connections.

Fig. 5 Step by step repairing strategy (Method-1)

Fig.6 Step by step repairing strategy (Method-2)

Experimental observations

The conditions of one of the deficient type-full size con-trol as well as rehabilitated specimens tested under two loading types are shown in Fig. 7. It may be observed that the specimens tested under load type-1 suffered more damage as compared to type-2. The degradation effect was understandably more under load type-1 due to more number of cycles at a particular displacement level. Typi-cal hysteretic responses obtained by plotting test data for rehabilitated specimens (BWF) of different sizes tested un-der loading type-1 are presented in Fig. 8. The averages of peak loads in the push and pull direction in the first cycle (load type-1) of each amplitude were calculated. The max-imum load as obtained by such averaging was considered as ultimate load carrying capacity of the specimens. Ulti-mate load carrying capacity of all the tested specimens is presented in Table 2. The results of control specimens are also presented in this table for comparison, where all the rehabilitated specimens are observed to show a slightly higher load carrying capacity than that of corresponding control specimen. It also shows that the appropriately cho-



sen repair strategy could retrieve back the lost capacity even for a severely damaged structural component.

Analysis of Results for Exploring the Presence of Size Effect

To explore the existence of size effect, the results obtained from testing of the specimens were analyzed. Equiva-lent stresses ( ) for all the specimens were calculated and bi-logarithmic plots were drawn. Various parameters, which are of practical relevance were also considered and the possible existence of size effects were investigated.

Bi-logarithmic Plot

The failure modes of BWF (both control and the reha-bilitated) specimens under consideration were in flexure. Hence, ultimate bending stress ( ) was calculated for all the specimens. Further, the failure modes of BWS and CWS control as well as the rehabilitated specimens were in shear. Therefore, ultimate shear stresses for these speci-mens were calculated. Using and characteristic di-mension (D), bi-logarithmic plots were drawn for control and rehabilitated specimens. The size effect law as pro-posed by Bažant [15] was used for the statistical regres-sion of the data. The mathematical expression of this law is given as:

(1)

B and are the two unknown constants which can be de-termined by statistical regression analysis. The value of tensile strength of concrete ( ) was calculated as per IS: 456 [12] and was taken as 2.504 N/mm2. To facilitate the evaluation of the constants in the size effect law, Eq. 1 can be rearranged as follows:

(2)

The above equation is of the form of Y = AX+C where and the constants C and A are given by

and , Hence value of B and are:

and D0= (3)

The calculated value of stress and other parameters nec-essary to carry out regression analysis and bi-logarithmic plotting for all the specimens are furnished in the Table 3. A typical regression plot of one of the deficiency types is shown in Fig. 9. The value of B and D0 using Eq. 3 were calculated from regression plot. Using these values, the bi-logarithmic plot were drawn with log (D/D0) in the X axis and log in the Y axis. The bi-logarithmic plots were drawn considering all the six data irrespective of the loading types. The bi-logarithmic plots for three types of rehabilitated and corresponding control specimens are furnished in Figs. 10 and 11 respectively. It is observed

Rehabilitated specimens Control specimens

Name of specimen Ultimate load carrying capacity (kN) Name of specimen Ultimate load carrying capacity (kN)

Specimens subjected to loading type-1

BWFLRe 84.085 BWFLC 73.285

BWFMRe 40.995 BWFMC 34.845

BWFSRe 11.890 BWFSC 9.885

BWSLRe 77.220 BWSLC 72.085

BWSMRe 38.665 BWSMC 34.190

BWSSRe 11.610 BWSSC 10.540

CWSLRe 64.635 CWSLC 58.010

CWSMRe 35.560 CWSMC 32.000

CWSSRe 9.895 CWSSC 8.046

Specimens subjected to loading type-2

BWFLRe 78.065 BWFLC 73.605

BWFMRe 39.250 BWFMC 35.995

BWFSRe 11.360 BWFSC 10.200

BWSLRe 80.970 BWSLC 74.060

BWSMRe 41.465 BWSMC 35.820

BWSSRe 11.820 BWSSC 9.840

CWSLRe 61.685 CWSLC 58.930

CWSMRe 32.840 CWSMC 31.230

CWSSRe 9.413 CWSSC 8.889Table 2 Ultimate load carrying capacity of specimens


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Table 3 Parameters for bi-logarithmic plotting


from these plots that the trend of the curve follows a hori-zontal line at the initial part, indicating no size effect. The curve approaches a straight line with slope of about -1/2 towards the end (LEFM zone). In the intermediate zone there is a smooth curved transitional part. Thus, it can be concluded that the plots show the presence of size effect in accordance with Bažant’s size effect law [15]. Further, size effect was observed to be more pronounced as the specimens behave in more and more brittle manner.

Size effect on energy dissipated per unit volume of D-region

To compare the energy dissipation of specimens having different sizes, specimen sizes were also correlated with

cumulative energy dissipated per unit volume. The D-re-gion of the connections as defined in ACI 318-08 [16] was considered in calculating the representative volume in a connection. The variation of with respect to drift angle for control and rehabilitated specimens tested under loading type-1 are shown in Figs. 12 and 13. It can be clearly ob-served that for both control and corresponding rehabili-tated specimens, the uppermost curve is for the smallest specimen, while the lowermost curve corresponds to the largest specimen. Similar trend was also observed for test results under loading type-2. It is thus observed that dur-ing cyclic loading, the energy dissipated per unit volume of the D-region of smaller specimen is more than that of the larger specimen and hence establishes its dependence on specimen size.


Size effect on stress variation with relative deflection

The relative displacements for different scaled models were calculated as the ratio of actual displacement to the scale of the model. Peak values of the load at each displacement cycle were used to calculate the equivalent stresses. Stress vs relative displacements under loading type-1 are shown in Figs.14 and 15 for control and reha-bilitated specimens respectively. These plots indicate that stresses for smallest specimen show highest values at all levels of relative displacement, while same are least for largest specimen. Similar trend was also observed for test results under loading type-2. Thus, it also supports the ex-istence of size effect in beam-column connections.

Fig. 7 Damage of BWFL specimens subjected to (a) loading type-1 and (b) loading type-2

(a) (b)

Fig. 8 Typical hysteretic responses

Fig. 9 Typical regression plot

Fig.10 Bi-logarithmic plot for rehabilitated specimens (a) BWF (b) BWS and (c) CWS

Fig.11 Bi-logarithmic plot for control specimens (a) BWF (b) BWS and (c) CWS


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Conclusions

The results obtained from test of thirty six numbers of RC beam-column connections (control and rehabilitated) were examined to explore the existence of size effect. Analyzed results were used for drawing bi-logarithmic plot. In all the cases, it was found that the bi-logarithmic plot followed the well established size effect law as proposed by Bažant [15]. It was also observed that the cumulative energy dis-sipated per unit volume of the D-region at every drift angle as well as the variation of stress with respect to relative de-flection exhibit their dependence on the size of specimens. Further, size effect was observed to be more prominent as the specimens behave in more and more brittle manner.

Fig. 12 Cumulative energy dissipated per unit volume of D-region for control specimens under loading type-1

Fig. 13 Cumulative energy dissipated per unit volume of D-region for rehabilitated specimens under loading type-1


Author Affiliation

Marthong C1, Dutta A2*, Deb S.K2

1Post-graduate Student, IIT Guwahati, Assam, India2Professor, Civil Engineering Department, IIT Guwahati, Assam, India*Corresponding Author

References

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Fig. 14 Stress versus relative deflection plot for control specimens under loading type-1

Fig. 15 Stress versus relative deflection plot for rehabilitated specimens under loading type-1

Journal of SEWC | March 2014��

2 Tsonos AG. Seismic rehabilitation of reinforced con-crete joints by removal and replacement technique. European Earthquake Engineering 2001; 3: 29-43.

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